When a server sends a third party invite another server may be the one
that the inviting user registers with. In this case it is that remote
server that will issue an actual invitation, and wants to do it "in the
name of" the original invitee. However, the new proper invite will not
be signed by the original server, and thus other servers would reject
the invite if it was seen as coming from the original user.

To fix this, a special case has been added to the auth rules whereby
another server can send an invite "in the name of" another server's
user, so long as that user had previously issued a third party invite
that is now being accepted.

Fix _delete_old_forward_extrem_cache query

Add total_room_count_estimate to /publicRooms

Notify on e2e events

Handle fact that _generate_room_entry may not return a room entry

Fix and clean up publicRooms pagination

Make public room search case insensitive

Add very basic filter API to /publicRooms

Change get_pos_of_last_change to return upper bound

Enable state caches on workers

Use stream_change cache to make get_forward_extremeties_for_room cache more effective