✨(fullstack) support everyone_can_mute room configuration

Introduce a new room setting controlling whether all participants,
including non-privileged users, can mute others.

Update API validation accordingly and add the frontend controls
allowing administrators to toggle the option and persist the
configuration through the API.

src/backend/core/api/serializers.py

@@ -329,6 +329,7 @@ class RoomConfiguration(BaseModel):
     """
 
     can_publish_sources: list[RoomConfigurationTrackSource] | None = None
+    everyone_can_mute: bool | None = None
 
     model_config = {"extra": "forbid"}