Currently we can implement only backend-specific filters (e.g., FinagleFilter) other than HTTP Endpoint/RPC.

To support backend-http server independent Endpoint/RPC testing (e.g., tests forHttpServerException, error responses, etc.), we need a filter adapter (e.g., filters written for HttpMessage.Request, Response, and F (abstraction for backend-specific Future), and translates it into FinagleFilter.

Then we can move filters like FinagleServer.errorFilter into Router.errorFilter.

http logging filter can be ported as well.