plugin XEP-0297: Reworked `forward` method and add bridge method: `Forward` method has been reworked and now includes a fallback. XEP-0297 ask to not use fallback, but following a discussion on xsf@, we agreed that this is a legacy thing and a fallback should nowadays be used, I'll propose a patch to the specification. A `message_forward` has been added to bridge. rel 461

this certificates are used to enable TLS during tests. Those must be the same as in
backend_e2e (they are generated there)