We assume, as we did before, that users bound their threepid to one of
the trusted identity servers. So we simply fill the new table with all
threepids in `user_threepids` joined with the trusted identity servers.
Due to the table locks taken out by the naive upsert, the table
statistics may be out of date. During deduplication it is important that
the correct index is used as otherwise a full table scan may be
incorrectly used, which can end up thrashing the database badly.
Currently we only have the one event format version defined, but this
adds the necessary infrastructure to persist and fetch the format
versions alongside the events.
We specify the format version rather than the room version as:
1. We don't necessarily know the room version, existing events may be
either v1 or v2.
2. We'd need to be careful to prevent/handle correctly if different
events in the same room reported to be of different versions, which
sounds annoying.
Allow for the creation of a support user.
A support user can access the server, join rooms, interact with other users, but does not appear in the user directory nor does it contribute to monthly active user limits.
