Log when we receive a /make_* request from a different origin

log when a redaction attempts to redact an event in a different room

There was some inconsistent behaviour in the caching layer around how
exceptions were handled - particularly synchronously-thrown ones.

This seems to be most easily handled by pushing the creation of
ObservableDeferreds down from CacheDescriptor to the Cache.

Bugfixes
--------

- Fix a regression introduced in v1.2.0rc1 which led to incorrect labels on some prometheus metrics. ([\#5734](https://github.com/matrix-org/synapse/issues/5734))

Log when we receive receipt from a different origin

`None` is not a valid event id, so queuing up a database fetch for it seems
like a silly thing to do.

I considered making `get_event` return `None` if `event_id is None`, but then
its interaction with `allow_none` seemed uninituitive, and strong typing ftw.

* Fix servlet metric names

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

* Remove redundant check

* Cover all return paths

* Add a prometheus metric for active cache lookups.

* changelog

* Allow Jaeger to be configured

* Update sample config

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

* Add decerators for tracing functions

* Use the new clean contexts

* Context and edu utils

* Move opentracing setters

* Move whitelisting

* Sectioning comments

* Better args wrapper

* Docstrings

Co-Authored-By: Erik Johnston <erik@matrix.org>

* Remove unused methods.

* Don't use global

* One tracing decorator to rule them all.

Add process hooks to tell systemd our state.

Mark flakey tests as blacklisted for worker mode

Speed up current state background update.

Don't package sytest-blacklist file.

Turns out that storing huge JSON arrays in the progress JSON isn't
something that postgres particularly likes.

I don't think its useful, and I don't even know where it would end up.

This also adds a worker blacklist.

This helps ensures that we only consider ourselves "up" once all the
startup functions have completed.

Cache get_version_string.

Fixes #5676.

Add `user_type` to returned fields in admin API user list endpoints

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

* Refactor Keyring._start_key_lookups

There's an awful lot of deferreds and dictionaries flying around here. The
whole thing can be made much simpler and achieve the same effect.

* Add a delay to key lookup lock release to fix stack overflow

A tactical call_later here should fix #5723

* changelog