Fix bug when invalidating destination retry timings

Fix error handling for missing auth_event

Fix error when logging incomplete requests

If a connection is lost before a request is read from Request, Twisted
sets `method` (and `uri`) attributes to dummy values. These dummy values
have incorrect types (i.e. they're not bytes), and so things like
`__repr__` would raise an exception.

To fix this we had a helper method to return the method with a
consistent type.

Avoid reraise, to improve stacktraces

Fix lazy loaded sync with rejected state events

Fix exceptions when handling incoming transactions

In particular, we assume that the name and canonical alias events in
the state have not been rejected. In practice this may not be the case
(though we should probably think about fixing that) so lets ensure that
we gracefully handle that case, rather than 404'ing the sync request
like we do now.

 Add a five minute cache to get_destination_retry_timings

Rewrite the dockerfile as a multistage build: this means we can get rid of a whole load of cruft which we don't need.

remove spurious federation checks on localhost

Remove redundant call to start_get_pdu_cache

I think this got forgotten in #3932. We were getting away with it because it
was the last call in this function.

Improve performance of getting typing updates for replication

Build and push docker image to hub automatically

Clarifications in FederationHandler

Run notify_app_services as a bg process

Replaced all occurences of e.message with str(e)

This test didn't do what it claimed to do, and what it claimed to do was the
same as test_cant_hide_direct_ancestors anyway.

This stuff is tested by sytest anyway.