Move voice-chat feature enabling toggle to the scene data

[pravusjif]

Currently Kernel sends a separate message telling the client that voice chat feature is enabled in the scene.

We should move this value to the scene data (in the scene JSON) so that we send this value to the cilent as the other values of the scene, using the same unified structure.

This was defined in this comment in an RFC as it will be consistent with future scene config values added in the scene JSON.