Ensure Element Call is the default for Video rooms where possible

[Half-Shot]

This refactors a bunch of things around using Element Call for video rooms, namely:

• element_call_video_rooms is now on by default, so that Video rooms do not default to Jitsi.
• If feature_video_rooms is off, users cannot enable element_call_video_rooms.
• If element_call.use_exclusively is on in the config.json, this setting is also forced on.

This still need ample tests, hence draft.

Checklist

• I have read through review guidelines and CONTRIBUTING.md.
• Tests written for new code (and old code if feasible).
• New or updated public/exported symbols have accurate TSDoc documentation.
• Linter and other CI checks pass.
• I have licensed the changes to Element by completing the Contributor License Agreement (CLA)