feat: implement static route

[francescovallone]

Description

A static route is a route that does not use the request context, but returns a result independently of it. In Serinus this can be achived creating a similar on method of the controller called onStatic and modifying the RouteData class to expose the isStatic flag.

The RequestHandler should also be modified to reflect this change. A static RouteData should be immediately resolved without passing from the handle function.

Requirements

• Add the onStatic method to the controller;
• Modify the documentation to reflect this change;
• Change the RouteData class;
• Change the behaviour of the RequestHandler;
• Add tests