[Spring Boot] Support Http Interface server-side

[wsalembi]

Http Exchange annotations which are the equivalent of MVC mapping annotations, can also be used server-side.

https://docs.spring.io/spring-framework/reference/integration/rest-clients.html#rest-http-service-client

On the server side, an @controller class can implement the same interface to handle requests with @HttpExchange controller methods.

Spring MVW (org.springframework.web.bind.annotation)	Spring Http Interface (org.springframework.web.service.annotation)
@RequestMapping	@HttpExchange
@GetMapping	@GetExchange
@PostMapping	@PostExchange
@PutMapping	@PutExchange
@PatchMapping	@PatchExchange
@DeleteMapping	@DeleteExchange

If you test rest-problem-java you'll notice there is an exception handler missing for org.springframework.web.method.annotation.HandlerMethodValidationException.

Draft HandlerMethodValidationExceptionHandler.java

[jpraet]

In which circumstances does HandlerMethodValidationException get thrown?

In #295 I added HttpExchange equivalents for the RestController to the Spring Boot integration tests, and everything still seems to work.