RIS: Implement initial dump signaling in ObserveFIB

cmd/ris/api/ris.pb.go

cmd/ris/api/ris.proto

cmd/ris/risserver/server.go

protocols/bgp/api/bgp.pb.go

protocols/bgp/server/update_sender.go

protocols/kernel/kernel.go

routingtable/adjRIBIn/adj_rib_in.go

routingtable/adjRIBOut/adj_rib_out.go

routingtable/client_interface.go

routingtable/client_manager_test.go

routingtable/locRIB/loc_rib.go

routingtable/mock_client.go