Inhibit propagation of user profile updates in m.room.member events

By default, when a Matrix user updates their display name or avatar URL, the server will send an m.room.member event with the updated profile information into every room where the user is a joined member. This is one of the most expensive operations in terms of server performance, just due to the number of events that may be generated. It is also wasteful, as the same info is replicated over and over into every room where the user is joined.

Instead, we have been working on transmitting user profile updates via the presence stream. This is part of the Matrix spec, but apparently had not been implemented until now.

Now that there is a better way to publish profile data, we should (optionally) tell the server not to also propagate profile data the old way in the m.room.member events. The fix seems to be to append ?propagate=false to the API requests when updating profile information. See MSC4069.