Permission system for broadcasts

### Your use case

#### What would you like to do?

I would like to be able to let only certain room members speak (or show their camera feed, or share their screen, etc) during a call, so that everyone else is only able to watch or listen to the call.

#### Why would you like to do it?

This could be useful for broadcasts - live audio or video feeds where only certain people can take active part, and everyone else is an audience.

#### How would you like to achieve it?

Whenever you start a call, there can be some sort of dropdown letting you choose who can participate in the call - either certain people, or everyone. If you choose the first option you get a dialogue that lets you select certain room members, and after the call starts there is another button letting you add or remove additional participants to the call.

### Have you considered any alternatives?

_No response_

### Additional context

_No response_