Allow assigning room admins using Admin API #22
Description
Please add a new button to the room view page (maybe to the members tab?) that allows making an arbitrary user as room admin.
That will allow restoring access to otherwise lost rooms (e.g., when you accidentally leave a room where you are the only admin).
The "make admin" button should show a modal window where you can enter arbitrary MXID, but by default, your own MXID should be shown as a placeholder (i.e., current Synapse Admin user)
This feature was already requested in Awesome-Technologies/synapse-admin#356, but at the time the original issue was created, the "Make Admin" API docs mentioned "The server administrator must be in the room and have permission to invite users." (that's no longer the case)