Some streams will occaisonally advance their positions without actually
having any new rows to send over federation. Currently this means that
the token will not advance on the workers, leading to them repeatedly
sending a slightly out of date token. This in turns requires the master
to hit the DB to check if there are any new rows, rather than hitting
the no op logic where we check if the given token matches the current
token.

This commit changes the API to always return an entry if the position
for a stream has changed, allowing workers to advance their tokens
correctly.

Allow invites via 3pid to bypass sender sig check

Support /initialSync in synchrotron worker

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