This PR refactors the app services component. It makes the following changes:
* Each appservice now gets its own NATS JetStream consumer
* The appservice database is now removed entirely, since we just use JetStream as a data source instead
* The entire component is now much simpler and we deleted lots of lines of code 💅
The result is that it should be much lighter and hopefully much more performant.
* Fix flakey sytest 'Local device key changes get to remote servers'
* Debug logs
* Remove internal/test and use /test only
Remove a lot of ancient code too.
* Use FederationRoomserverAPI in more places
* Use more interfaces in federationapi; begin adding regression test
* Linting
* Add regression test
* Unbreak tests
* ALL THE LOGS
* Fix a race condition which could cause events to not be sent to servers
If a new room event which rewrites state arrives, we remove all joined hosts
then re-calculate them. This wasn't done in a transaction so for a brief period
we would have no joined hosts. During this interim, key change events which arrive
would not be sent to destination servers. This would sporadically fail on sytest.
* Unbreak new tests
* Linting
