Add new service annotation - `@Method(GET|POST|PUT|...)`

[artem-v]

Add support of optional service annotation @Method with value as HTTP method. Must be defined only on methods with annotation @ServiceMethod.

Idea is to support clients who wants to call scalecube service through the HTTP gateway and to support http methods RESTful semantic.

Expected changes

• There must be new enum type in scalecube-services-api with all http methods.
• ServiceReference, ServiceMethodDefinition objects must have method field (optional).
• Add logic to our "out-of-the-box" routers (RandomServiceRouter and RoundRobinServiceRouter) so they begin to support method in the routing logic.

Depends on

https://github.com/scalecube/scalecube-services/issues/856