This adds a new backfill type for media that sends a request to the
phone for every media that is not available on the WA servers. WA
deletes media from their servers after about two weeks, so you have to
ask the phone to re-upload it.
In order to use this, you need to enable
bridge.history_sync.backfill_media and configure the requests that will
be made per portal using bridge.history_sync.media (which is similar to
the deferred backfill config).
If you already have backfilled portals, but want to do a one-off media
backfill for all existing portals, you can set
bridge.history_sync.enqueue_backfill_media_next_start to true.
bridge.history_sync.max_initial_conversations:
This setting determines the maximum number of initial conversations
that should be backfilled. The data for all the other conversations
will be stored in the database for backfill at a later time.
bridge.history_sync.immediate:
These settings are for the initial backfill that should be performed
to populate each of the initial chats with a few messages so that
users can continue their conversations without loosing context.
bridge.history_sync.deferred:
These settings are for backfilling the rest of the chat history that
was not covered by the immediate backfills. These should generally be
done at a slower pace to avoid overloading the homeserver.
