Allow tracking puppeted users for MAU (#11561)

Currently when puppeting another user, the user doing the puppeting is
tracked for client IPs and MAU (if configured).

When tracking MAU is important, it becomes necessary to be possible to
also track the client IPs and MAU of puppeted users. As an example a
client that manages user creation and creation of tokens via the Synapse
admin API, passing those tokens for the client to use.

This PR adds optional configuration to enable tracking of puppeted users
into monthly active users. The default behaviour stays the same.

Signed-off-by: Jason Robinson <jasonr@matrix.org>