Added mute video moderation feature

[skolmer]

This change adds the ability for a moderator to deactivate the camera of other participants. The implementation uses the same approach that was implemented to mute audio of other participants.

This feature consists of multiple PRs:

• https://github.com/jitsi/jitsi-media-transform/pull/327
• https://github.com/jitsi/jitsi-videobridge/pull/1569
• https://github.com/jitsi/jitsi-xmpp-extensions/pull/37
• https://github.com/jitsi/jicofo/pull/695
• https://github.com/jitsi/lib-jitsi-meet/pull/1496
• https://github.com/jitsi/jitsi-meet/pull/8630