Create an Admin API to remove a local user from non-public rooms in a space

[callahad]

While we await proper, Spec-based tools for controlling permissions within a Space, it would be a nice stopgap to build an ad hoc Admin API which:

• Accepts a local MXID and Space ID
• Removes the given user from all non-public rooms in that space and its sub-spaces, including the space itself.

By constraining this to local users, the server can initiate the leave directly, without needing an admin or moderation bot in each room.

[clokep]

non-public rooms

Can we be a bit more specific about what this means? I assume it means rooms that do not have join_rules = public, but I'm not sure.

What happens if a "normal" room is given instead of a space?

[callahad]

I assume it means rooms that do not have join_rules = public, but I'm not sure.

That's what I'm thinking. We could remove them from every channel in the space, but that might be unnecessarily disruptive / the wrong tool for the job.

What happens if a "normal" room is given instead of a space?

Remove the user from that room (assuming it's not public) and we're done

[dklimpel]

Related to #11358

[DMRobertson]

This is presumably still useful but not urgently required?