Fetch Element call settings from the homeserver

### Your use case

#### What would you like to do?

I would like to be able to adjust the following settings, per homeserver:
- disable video when the call starts (it's on now)
- disable loudspeaker by default on the phone (it's on now)
- enable ringing the call on group chats (it's off now)

Ideally - all other settings as well: quality settings, etc (once implemented)

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

For the moment, Element Call seems like created more for the conferences in isolated environment, not for the regular calls. Guess it's fine for some use cases, but not that much for others.

Element X team believe it shall be implemented on Element Call side ([ref](https://github.com/element-hq/element-x-ios/issues/4813#issuecomment-3641168928)).

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

I believe the reading of element.json or some other kind of pre-defined / structure from the server shall work fine.

### Have you considered any alternatives?

I've considered rebuild the app - but it's quite complicated + Apple doesn't make it easy to publish as well, especially, since Element contains strong encryption.

### Additional context

From what I know, that is a very popular requests - disable video, loudspeaker + I can recall there was a PR enabling group calls - people need it, as the working environment and conditions are quite different.

Looks like ability to configure the EC from the server, as per requirements, shall be quite easy.

Happy to prepare a PR, given the confirmation that is is acceptable overall and / or some instructions what are the preferred ways to do that.