Allow for additional fields in JWT token to enable the use lobby if not authenticated

[eyck]

To enable the use of Jitsi/Prosody plugins like token_lobby_bypass (https://github.com/jitsi-contrib/prosody-plugins/tree/main/token_lobby_bypass) some more fields in the JWT should be configurable. In the case of token_lobby_bypass the token element context.user.lobby_bypass should be set to true if the user is authenticated in NextCloud. In this case the user does not have to wait in the Jitsi lobby e.g. when the prosody plugin lobby_autostart ist active.