plugin XEP-0077, XEP-0100: Adapt to component, and modernize: - Plugin XEP-0077 can now be used with component, allowing to register methods to return registration form, and to (un)register. - Plugin XEP-0077 now advertises its feature in disco. - Plugin XEP-0100 has been modernized a bit: it is one of the older plugin in Libervia, and it has now some type hints, models and async methods. - Plugin XEP-0100's bridge method `gateways_find` now returns a serialised dict with relevant data. Former XMLUI version has been moved to `gateways_find_xmlui`. rel 449