XX-2856 / Gateway <-> Server ping and permissioning address

Makefile

gateway/connectivity.go

gateway/getPermissioningAddress.go

gateway/getPermissioningAddress_test.go

gateway/handler.go

go.mod

go.sum

mixmessages/mixmessages.pb.go

mixmessages/mixmessages.proto

mixmessages/ndf_test.go

mixmessages/roundError_test.go

mixmessages/roundInfo_test.go

network/instance_test.go

network/securedNdf_test.go

node/endpoint.go

node/handler.go