🔧(frontend) pass dynamically the LiveKit url

It seems appropriate that backend owns the responsability of knowing any
information/configurations of the LiveKit server. Then, it shares those
with the frontend.

Please see my previous commit to understand why environment variables are
not appropriate for deployment in several remove environments.

As of today, the LiveKit server URL is the only configuration exposed
dynamically to the frontend. Thus, it doesn't justify adding a new route
to the API, responsible for exposing configurations (e.g. /configuration).

As the frontend needs to call the backend when it wants to initiate a new
webconference room, let's pass the server URL when retrieving the room's token.
It is relevant, to get both the room location and the keys to open the room in
the same call.

I prefered to be pragmatic, if the need appears any soon, I would refactor
these parts.

env.d/development/common.dist

@@ -43,3 +43,4 @@ OIDC_AUTH_REQUEST_EXTRA_PARAMS={"acr_values": "eidas1"}
 # Livekit Token settings
 LIVEKIT_API_SECRET="secret"
 LIVEKIT_API_KEY="devkey"
+LIVEKIT_API_URL=http://localhost:7880