Solve In-Band Vetting with Matrix Policy Gateway

[MilkManzJourDaddy]

Originally filed under In-Band Vetting Prior to Unrestricted MXID Whitelisting and explored to no avail in [Solve In-Band Vetting with Matrix-Corporal](Created issue: devture/matrix-corporal#1).

The idea is to limit a MXID from initally being able to do anything but send events/messages into a force-join room for vetting, i.e. one set in: homeserver.yaml via adding: auto_join_rooms: ["#SomeRoom:HomeServer.TLD"].

After Homeserver it is decided to grant the user unrestristricted use, the MXID may be used normally and freely join other rooms on the Homeserver, and Federated rooms if the Homeserver federates.