api: add static router and improve path parser in rpc handler (#1437)

* api: add static router and improve path parser in rpc handler

Signed-off-by: Vasiliy Tolstov <v.tolstov@unistack.org>

* expose metadata context key to be able to get unmodified map keys

Signed-off-by: Vasiliy Tolstov <v.tolstov@unistack.org>

* server/grpc: fix jsonpb codec for protobuf msg

Signed-off-by: Vasiliy Tolstov <v.tolstov@unistack.org>

* api/handler/rpc: write 204 status code when rsp is nil

Signed-off-by: Vasiliy Tolstov <v.tolstov@unistack.org>

* api/handler/rpc: add check for nil response for non javascript

Signed-off-by: Vasiliy Tolstov <v.tolstov@unistack.org>

registry.go

@@ -250,6 +250,14 @@ func (r *registryRouter) Close() error {
 	return nil
 }
 
+func (r *registryRouter) Register(ep *api.Endpoint) error {
+	return nil
+}
+
+func (r *registryRouter) Deregister(ep *api.Endpoint) error {
+	return nil
+}
+
 func (r *registryRouter) Endpoint(req *http.Request) (*api.Service, error) {
 	if r.isClosed() {
 		return nil, errors.New("router closed")