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>

api/router/router.go

@@ -15,6 +15,10 @@ type Router interface {
 	Close() error
 	// Endpoint returns an api.Service endpoint or an error if it does not exist
 	Endpoint(r *http.Request) (*api.Service, error)
+	// Register endpoint in router
+	Register(ep *api.Endpoint) error
+	// Deregister endpoint from router
+	Deregister(ep *api.Endpoint) error
 	// Route returns an api.Service route
 	Route(r *http.Request) (*api.Service, error)
 }