Bring matrix-org-hotfixes changes into mainline

[erikjohnston]

There aren't many changes, so we may as well move the rest into mainline (behind config flags or whatever)

[ShadowJonathan]

I got a diff here for the current (22-4-2021) changes in -hotfixes that aren't in develop.

[DMRobertson]

State of play as I see it today:

• 2017/05/23: e5537cf98333b428dbc481ed443daed2f0cfa074 and introduced a member_limiter on the
  RoomMemberHandler, later tweaked by subsequent commits. This wraps the call to update_membership_locked.
  • Formalised in Limit concurrent AS joins #11996
• 2017/10/12: fae708c0e8c35930f1172322b7c0e9f0b1b3f9a4 from matrix-appservice-irc#506 suppresses the requirement that application services can only lookup joined members if they control a user which is already in this room.
  • Hotfixes: revert room members hack #13598 addresses this.
• 2018/02/14: 66dcbf47a36b5ca0e88d4658578d6fb5e6dbd910 disables auto search for prefixes in event search.
  • Unified search query syntax using the full-text search capabilities of the underlying DB #11635 removed this (merged in 03ba8c8)
  • Had to revert this in 37307a5 because we suspected the FTS stuff contributed to DB slowness.
  • As of 2022/02/10 this doesn't seem to exist any more, presumably since Unified search query syntax using the full-text search capabilities of the underlying DB #11635.
• 2018/02/14: 8f8ea91eefcc43c5ac24e85b14a86af4da53e6e0 bumps client_ip LAST_SEEN_GRANULARITY from 2 to 10 minutes.
• 2018/06/04: 9e38981ae47d03467a954c3c540c51b567f6e50b and subsequent commits send http pushes directly to a local address, rather than via cloudflare.
• 2018/07/02: ca21957b8a4942e829050834297afb290338c120 adds hardcoded timeouts when processing membership updates to prevent inflight requests from stacking up (later tweaked to 80s by a subsequent commit).
• 2021/12/15--2023/02/02: various changelogs left on the branch. Not cleaned up by a merge, maybe?
  • fixed by 4d2d701 and e984b6f
• 2022/01/07: 5cc41f1b05416954f4c9e7aea1df308f4a451abe introduces debug logging
  • fixed by Hotfixes: Revert commit() OpenTracing hackery #11906
• 2022/02/08: Printf debugging for MSISDN validation #11882 adds some debug logging related to MSISDNs.
  • Apply logging from hotfixes branch to develop #15054
• 2022/11/22: 5436c3e ignores device list updates for users with excessive numbers of devices.