* Fix spec compliance; tweaks without values are valid

(default to True, which is only concretely specified for
`highlight`, but it seems only reasonable to generalise)

* Changelog for 7766.

* Add documentation to `tweaks_for_actions`

May as well tidy up when I'm here.

* Add a test for `tweaks_for_actions`

The CI appears to use the latest version of isort, which is a problem when isort gets a major version bump. Rather than try to pin the version, I've done the necessary to make isort5 happy with synapse.

fixes #7016

* Remove obsolete comment about ancient temporary code

Signed-off-by: Olivier Wilkinson (reivilibre) <olivier@librepush.net>

* Implement hack to set push priority

based on whether the tweaks indicate the event might cause
effects.

* Changelog for 7765

Signed-off-by: Olivier Wilkinson (reivilibre) <olivier@librepush.net>

* Antilint

* Add tests for push priority

Signed-off-by: Olivier Wilkinson (reivilibre) <olivier@librepush.net>

* Update synapse/push/httppusher.py

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

* Antilint

* Remove needless invites from tests.

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

State res v2 across large data sets can be very CPU intensive, and if
all the relevant events are in the cache the algorithm will run from
start to finish within a single reactor tick. This can result in
blocking the reactor tick for several seconds, which can have major
repercussions on other requests.

To fix this we simply add the occaisonal `sleep(0)` during iterations to
yield execution until the next reactor tick. The aim is to only do this
for large data sets so that we don't impact otherwise quick resolutions.=

This ended up being a bit more invasive than I'd hoped for (not helped by
generic_worker duplicating some of the code from homeserver), but hopefully
it's an improvement.

The idea is that, rather than storing unstructured `dict`s in the config for
the listener configurations, we instead parse it into a structured
`ListenerConfig` object.

Fixes https://github.com/matrix-org/synapse/issues/7683

Broke in: #7649

We had a `yield` acting on a coroutine. To be fair this one is a bit difficult to notice as there's a function in the middle that just passes the coroutine along.

Fixes https://github.com/matrix-org/synapse/issues/2431

Adds config option `encryption_enabled_by_default_for_room_type`, which determines whether encryption should be enabled with the default encryption algorithm in private or public rooms upon creation. Whether the room is private or public is decided based upon the room creation preset that is used.

Part of this PR is also pulling out all of the individual instances of `m.megolm.v1.aes-sha2` into a constant variable to eliminate typos ala https://github.com/matrix-org/synapse/pull/7637

Based on #7637

Fixes https://github.com/matrix-org/synapse/issues/3177

Allow new users to be registered via the admin API even if the monthly active user limit has been reached (#7263)

- Admin is able to
  - change displaynames
  - delete devices
  - list devices
  - get device informations

Fixes #7330

Closes #4382

Signed-off-by: Maxim Plotnikov <wgh@torlan.ru>

While working on https://github.com/matrix-org/synapse/issues/5665 I found myself digging into the `Ratelimiter` class and seeing that it was both:

* Rather undocumented, and
* causing a *lot* of config checks

This PR attempts to refactor and comment the `Ratelimiter` class, as well as encourage config file accesses to only be done at instantiation. 

Best to be reviewed commit-by-commit.

@uhoreg has confirmed these were both typos. They are only in comments and tests though, rather than anything critical.

Introduced in:

* https://github.com/matrix-org/synapse/pull/7157
* https://github.com/matrix-org/synapse/pull/5726

Calls `self.get_success` on all deferred methods instead of abusing `self.pump()`. This has the benefit of working with coroutines, as well as checking that method execution completed successfully.

There are also a few small cleanups that I made in the process.

It looks like `user_device_resync` was ignoring cross-signing keys from the results received from the remote server. This patch fixes this, by processing these keys using the same process `_handle_signing_key_updates` does (and effectively factor that part out of that function).

This mostly applise to `*stateGroupCache*` and co.

Broke in #6391.

This is already correctly done when we instansiate the cache, but wasn't
when it got reloaded (which always happens at least once on startup).

A couple of changes of significance:

 * remove the `_last_ack < federation_position` condition, so that
   updates will still be correctly processed after restart

 * Correctly wire up send_federation_ack to the right class.