Update backward extremity docs to make it clear that it does not indicate whether we have fetched an events' `prev_events` (#11469)

Spawning from https://github.com/matrix-org/synapse/pull/9445#discussion_r758958181



Co-authored-by: Richard van der Hoff <1389908+richvdh@users.noreply.github.com>

* move wiki pages to synapse/docs and add a few titles where necessary

* update SUMMARY.md with added pages

* add changelog

* move incorrectly located newsfragment

* update changelog number

* snake case added files and update summary.md accordingly

* update issue/pr links

* update relative links to docs

* update changelog to indicate that we moved wiki pages to the docs and state reasoning

* requested changes to admin_faq.md

* requested changes to database_maintenance_tools.md

* requested changes to understanding_synapse_through_graphana_graphs.md

* add changelog

* fix leftover merge errata

* fix unwanted changes from merge

* use two spaces between entries

* outdent code blocks

* move wiki pages to synapse/docs and add a few titles where necessary

* update SUMMARY.md with added pages

* add changelog

* move incorrectly located newsfragment

* update changelog number

* snake case added files and update summary.md accordingly

* update issue/pr links

* update relative links to docs

* update changelog to indicate that we moved wiki pages to the docs and state reasoning

* revert unintentional change to CHANGES.md

* add link

Co-authored-by: Andrew Morgan <1342360+anoadragon453@users.noreply.github.com>

* Update CHANGES.md

Co-authored-by: Andrew Morgan <1342360+anoadragon453@users.noreply.github.com>

Co-authored-by: Andrew Morgan <1342360+anoadragon453@users.noreply.github.com>

fix header level

Dex isn't yet [1,2] a certified OpenID Provider implementation. As of today, it's not on the list maintained by the OpenID Foundation. [3]

[1] https://github.com/dexidp/dex/issues/42
[2] https://github.com/dexidp/dex/issues/262
[3] https://openid.net/certification/

* Add note to postgres doc about hugepages

* Newsfragment

Co-authored-by: Sean Quah <8349537+squahtx@users.noreply.github.com>

This also makes additional updates where the implementation
had drifted from the approved MSC.

Unstable endpoints will be removed at a later data.

Co-authored-by: Brendan Abolivier <babolivier@matrix.org>

Allows specifying a different claim (from the default "sub") to use
when calculating the localpart of the Matrix ID used during the
JWT login.

Instead of having admins poke into the database directly.

Can currently run jobs to populate stats and to populate
the user directory.

Otherwise I get this beautiful stacktrace:

```
python3 -m synapse.app.homeserver --config-path /etc/matrix/homeserver.yaml
Traceback (most recent call last):
  File "/usr/lib/python3.8/runpy.py", line 194, in _run_module_as_main
    return _run_code(code, main_globals, None,
  File "/usr/lib/python3.8/runpy.py", line 87, in _run_code
    exec(code, run_globals)
  File "/root/synapse/synapse/app/homeserver.py", line 455, in <module>
    main()
  File "/root/synapse/synapse/app/homeserver.py", line 445, in main
    hs = setup(sys.argv[1:])
  File "/root/synapse/synapse/app/homeserver.py", line 345, in setup
    config = HomeServerConfig.load_or_generate_config(
  File "/root/synapse/synapse/config/_base.py", line 671, in load_or_generate_config
    config_dict = read_config_files(config_files)
  File "/root/synapse/synapse/config/_base.py", line 717, in read_config_files
    yaml_config = yaml.safe_load(file_stream)
  File "/root/synapse/env/lib/python3.8/site-packages/yaml/__init__.py", line 125, in safe_load
    return load(stream, SafeLoader)
  File "/root/synapse/env/lib/python3.8/site-packages/yaml/__init__.py", line 81, in load
    return loader.get_single_data()
  File "/root/synapse/env/lib/python3.8/site-packages/yaml/constructor.py", line 49, in get_single_data
    node = self.get_single_node()
  File "/root/synapse/env/lib/python3.8/site-packages/yaml/composer.py", line 36, in get_single_node
    document = self.compose_document()
  File "/root/synapse/env/lib/python3.8/site-packages/yaml/composer.py", line 55, in compose_document
    node = self.compose_node(None, None)
  File "/root/synapse/env/lib/python3.8/site-packages/yaml/composer.py", line 84, in compose_node
    node = self.compose_mapping_node(anchor)
  File "/root/synapse/env/lib/python3.8/site-packages/yaml/composer.py", line 133, in compose_mapping_node
    item_value = self.compose_node(node, item_key)
  File "/root/synapse/env/lib/python3.8/site-packages/yaml/composer.py", line 82, in compose_node
    node = self.compose_sequence_node(anchor)
  File "/root/synapse/env/lib/python3.8/site-packages/yaml/composer.py", line 110, in compose_sequence_node
    while not self.check_event(SequenceEndEvent):
  File "/root/synapse/env/lib/python3.8/site-packages/yaml/parser.py", line 98, in check_event
    self.current_event = self.state()
  File "/root/synapse/env/lib/python3.8/site-packages/yaml/parser.py", line 379, in parse_block_sequence_first_entry
    return self.parse_block_sequence_entry()
  File "/root/synapse/env/lib/python3.8/site-packages/yaml/parser.py", line 384, in parse_block_sequence_entry
    if not self.check_token(BlockEntryToken, BlockEndToken):
  File "/root/synapse/env/lib/python3.8/site-packages/yaml/scanner.py", line 116, in check_token
    self.fetch_more_tokens()
  File "/root/synapse/env/lib/python3.8/site-packages/yaml/scanner.py", line 227, in fetch_more_tokens
    return self.fetch_alias()
  File "/root/synapse/env/lib/python3.8/site-packages/yaml/scanner.py", line 610, in fetch_alias
    self.tokens.append(self.scan_anchor(AliasToken))
  File "/root/synapse/env/lib/python3.8/site-packages/yaml/scanner.py", line 922, in scan_anchor
    raise ScannerError("while scanning an %s" % name, start_mark,
yaml.scanner.ScannerError: while scanning an alias
  in "/etc/matrix/homeserver.yaml", line 614, column 5
expected alphabetic or numeric character, but found '.'
  in "/etc/matrix/homeserver.yaml", line 614, column 6
```

Signed-off-by: Nicolai Søborg <git@xn--sb-lka.org>

* Add support for `/_matrix/media/v3` APIs

Signed-off-by: Aaron Raimist <aaron@raim.ist>

* Update `workers.md` to use v3 client and media APIs

Signed-off-by: Aaron Raimist <aaron@raim.ist>

* Add changelog

Signed-off-by: Aaron Raimist <aaron@raim.ist>

Signed-off-by: Ashwin S. Nair <58840757+Ashwin-exe@users.noreply.github.com>

Signed-off-by: Dirk Klimpel <dirk@klimpel.org>

Co-authored-by: Dirk Klimpel <5740567+dklimpel@users.noreply.github.com>
Co-authored-by: Andrew Morgan <1342360+anoadragon453@users.noreply.github.com>

Fixes #11259

We might as well use a default value for `public_baseurl` based on
`server_name` - in many cases, it will be correct.

Port 5349, not 5479.

* Remove unused Vagrant scripts

* Change package Architecture to any

* Preinstall the wheel package when building venvs.

Addresses the following warnings during Debian builds:

    Using legacy 'setup.py install' for jaeger-client, since package 'wheel' is not installed.
    Using legacy 'setup.py install' for matrix-synapse-ldap3, since package 'wheel' is not installed.
    Using legacy 'setup.py install' for opentracing, since package 'wheel' is not installed.
    Using legacy 'setup.py install' for psycopg2, since package 'wheel' is not installed.
    Using legacy 'setup.py install' for systemd-python, since package 'wheel' is not installed.
    Using legacy 'setup.py install' for pympler, since package 'wheel' is not installed.
    Using legacy 'setup.py install' for threadloop, since package 'wheel' is not installed.
    Using legacy 'setup.py install' for thrift, since package 'wheel' is not installed.

* Allow /etc/default/matrix-synapse to be missing

Per the systemd.exec manpage, prefixing an EnvironmentFile with "-":

> indicates that if the file does not exist, it will not be read and no
> error or warning message is logged.

Signed-off-by: Dan Callahan <danc@element.io>

Co-authored-by: David Robertson <david.m.robertson1@gmail.com>
Co-authored-by: Julian Vanden Broeck <julian.vandenbroeck@dalibo.com>

Fixes: #10874
Signed-off-by: Dirk Klimpel <dirk@klimpel.org>

Make `check_event_allowed` module API callback not fail open (accept events) when an exception is raised (#11033)

Remove deprecated delete room admin API,
`POST /_synapse/admin/v1/rooms/<room_id>/delete`

Fixes https://github.com/matrix-org/synapse/issues/8308

* Labeled a lot more code blocks with the appropriate type
* Fixed a couple of minor typos (missing/extraneous commas)

Signed-off-by: Sumner Evans <me@sumnerevans.com>