Implement VoiceService.{i}.SIP.Network.{i}.FQDNServer.{i}., REF 15305

The previous implementation of FQDNServer. is removed since it supported FQDNServer.Origin = Static, but according to DT requirement we have to support "AutoConfigured" only. It means that we do not need to save any configuration to uci, "set" requests will be skipped. We only retrieve the current data from asterisk (SRV reply) and propagate it to the TRs. Relevant MRs: asterisk!263 (merged) asterisk-chan-voicemngr!104 (merged)