Profile /messages and make it faster v1

[kittykat]

Message history can be very slow to load. Users expect to be able to rapidly load scrollback within a room, infinite scrolling without having to wait for the server to load more messages.

Relevant milestones:

• Q4 milestones

These tasks need to be completed for this issue to be closed:

• filter_events_for_client is time-consuming and expensive #14108
• get_bundled_aggregations takes a few seconds even when there is no relations #13624
• CS-API /messages requests fail on develop when using postgres due to NumericValueOutOfRange if some events have repeatedly failed to backfill #13929
• have_seen_event cache is not invalidated when we persist an event #13856
• Only try to backfill event if we haven't tried before recently #13622
• Keep track when we try to backfill an event #13621
• Optimize how we calculate likely_domains during backfill #13626

[kittykat]

@MadLittleMods Do you have any thoughts on how much more improvement can be made here with the remaining open issues?

[MadLittleMods]

@kittykat Maybe down to ~10s. #13623 and #13619 would help make our numbers more consistent. #13620 would be a general nice win for federation traffic.

[kittykat]

Follow on tasks split out into #15182