This method only has heartbeat session population logic for now, so it's
actually a no-op during provisioning. However, there's probably some
value in "mandating" that clients call this shortly after construction,
so we have a chance to run any setup logic that we might need in the
future.
This _feels_ unidiomatic...?
This comment seems to imply that specifying this function is a shortcut
of sorts, when it's actually required and mautrix-go doesn't fallback to
the connector in the way described.
