Some sort of way to ban a user (possibly ip address) from the call

### Your use case

I believe this could prove useful as the only way right now to "kick" a user is to create another call and not give them the link.

### Have you considered any alternatives?

No

### Additional context

n/a

No files, tests, or entry points are named. Start by tracing how users join a call and how the existing call-creation workaround removes access; clarify whether banning should target a Matrix user, an IP address, or both. Done should mean an agreed scope and a defined way for a call participant to be prevented from rejoining.

Written by the indexing model from the issue text.