Initial support for getting SFO config using OIDC

* Change `jwt_service_url` to `livekit_service_url`
 * Make it a POST so we can send the openID token sensibly
 * Get an OIDC token & pass it with the request
 * Read the SFU URL from there too

and convert the auth server accordingly, althugh with no actual OIDC
support yet, it just issues tokens blindly just as before and ignores
the openid token completely.

We'll need to update configs & the JWT service before merging this.

src/config/ConfigOptions.ts

@@ -55,10 +55,8 @@ export interface ConfigOptions {
 
   // Describes the LiveKit configuration to be used.
   livekit?: {
-    // The LiveKit server URL to connect to.
-    server_url: string;
-    // The link to the service that generates JWT tokens to join LiveKit rooms.
-    jwt_service_url: string;
+    // The link to the service that returns a livekit url and token to use it
+    livekit_service_url: string;
   };
 
   /**