Implement MSC3852: Expose `last_seen_user_agent` to users for their own devices; also expose to Admin API (#13549)

Uses Redis replication in additional test cases (instead of
TCP replication). A small step towards dropping TCP replication.

Fix validation problem that occurs when a user tries to deactivate their account or change their password. (#13563)

Follow-up to https://github.com/matrix-org/synapse/pull/13533

Part of https://github.com/matrix-org/synapse/issues/13356

Signed-off-by: Sean Quah <seanq@matrix.org>

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

Track number of hosts affected by the rate limiter so we can differentiate one really noisy homeserver from a general ratelimit tuning problem across the federation.

Follow-up to https://github.com/matrix-org/synapse/pull/13534

Part of https://github.com/matrix-org/synapse/issues/13356

Closes #13415.

Signed-off-by: Ayush Anand <iamayushanand@gmail.com>

Use a state filter or accept partial state in a few places where we
request state, to avoid blocking.

To make lazy-loading `/sync`s work, we need to provide the memberships
of event senders, which are not guaranteed to be in the room state.
Instead we dig through auth events for memberships to present to
clients. The auth events of an event are guaranteed to contain a
passable membership event, otherwise the event would have been rejected.

Note that this only covers the common code paths encountered during
testing. There has been no exhaustive checking of all sync code paths.

Fixes #13146.

Signed-off-by: Sean Quah <seanq@matrix.org>

Related to https://github.com/matrix-org/synapse/pull/13499

Part of https://github.com/matrix-org/synapse/issues/13356

Fix a bug in the `/event_reports` Admin API which meant that the total count could be larger than the number of results you can actually query for. (#13525)

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

Broke by #13522

It looks like we have some rules in the DB with a priority class less
than 0 that don't override the base rules. Before these were just
dropped, but #13522 made that a hard error.

Instrument the federation/backfill part of `/messages` so it's easier to follow what's going on in Jaeger when viewing a trace.

Split out from https://github.com/matrix-org/synapse/pull/13440

Follow-up from https://github.com/matrix-org/synapse/pull/13368

Part of https://github.com/matrix-org/synapse/issues/13356

Synapse does not currently support faster room joins on deployments with
workers.

Signed-off-by: Sean Quah <seanq@matrix.org>

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

This improves load times for push rules:

| Version              | Time per user | Time for 1k users | 
| -------------------- | ------------- | ----------------- |
| Before               |       138 µs  |             138ms |
| Now (with custom)    |       2.11 µs |            2.11ms |
| Now (without custom) |       49.7 ns |           0.05 ms |

This therefore has a large impact on send times for rooms
with large numbers of local users in the room.

Use Pydantic to systematically validate a first batch of endpoints in `synapse.rest.client.account`. (#13188)

Instrument FederationStateIdsServlet - `/state_ids` so it's easier to follow what's going on in Jaeger when viewing a trace.

This reverts commit f383b9b3. Other PRs
were seeing mypy failures that looked to be related to mypy-zope.
Confusingly, we didn't see this on #13521.

Revert this for now and investigate later.

* Clarifies comments.
* Fixes an erroneous comment (about return type) added in #13455
  (ec248132).
* Clarifies the name of a variable.
* Simplifies logic of pulling out the latest join for the requesting user.

Signed-off-by: James Barton <james@neodon.com>

Add note to `redaction_retention_period` documentation mentioning that event purging runs at most every 5m (#13492)

Events can be un-rejected or newly-rejected during resync, so ensure we update
the database and caches when that happens.