* 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.
