✨(backend) add 'username' query param when retrieving a room

Quick and dirty approach. It works, that's essential.
Frontend can pass a desired username for the user. This would
be the name displayed in the room to other participants.
Usernames don't need to be unique, but user identities do

If no username is passed, API will fall back to a default username.
Why? This serves as a security mechanism. If the API is called
incorrectly by a client, it maintains the previous behavior.

src/backend/core/api/serializers.py

@@ -122,10 +122,14 @@ class RoomSerializer(serializers.ModelSerializer):
         if role is not None or instance.is_public:
             slug = f"{instance.id!s}".replace("-", "")
 
+            username = request.GET.get("username", None)
+
             output["livekit"] = {
                 "url": settings.LIVEKIT_CONFIGURATION["url"],
                 "room": slug,
-                "token": utils.generate_token(room=slug, user=request.user),
+                "token": utils.generate_token(
+                    room=slug, user=request.user, username=username
+                ),
             }
 
         output["is_administrable"] = is_admin

src/backend/core/api/viewsets.py

@@ -188,12 +188,15 @@ class RoomViewSet(
             if not settings.ALLOW_UNREGISTERED_ROOMS:
                 raise
             slug = slugify(self.kwargs["pk"])
+            username = request.query_params.get("username", None)
             data = {
                 "id": None,
                 "livekit": {
                     "url": settings.LIVEKIT_CONFIGURATION["url"],
                     "room": slug,
-                    "token": utils.generate_token(room=slug, user=request.user),
+                    "token": utils.generate_token(
+                        room=slug, user=request.user, username=username
+                    ),
                 },
             }
         else: