Add Open-telemetry support (#517)

This PR brings open-telemetry metrics to the
Management service.
The Management service exposes new HTTP endpoint
/metrics on 8081 port by default.
The port can be changed by specifying
--metrics-port PORT flag when starting the service.

management/server/http/middleware/jwtmiddleware.go

@@ -186,7 +186,7 @@ func (m *JWTMiddleware) CheckJWTFromRequest(w http.ResponseWriter, r *http.Reque
 
 	validatedToken, err := m.ValidateAndParse(token)
 	if err != nil {
-		m.Options.ErrorHandler(w, r, "The token isn't valid")
+		m.Options.ErrorHandler(w, r, err.Error())
 		return err
 	}