[Backport 12.2] Handling unsupported HttpMethods in provided ResourceResolvers

In the bundled ResourceResolver implementations (SimpleJacksonRestTemplateResourceResolver and SimpleJdomRestTemplateResourceResolver), only "GET" and "POST" HTTP methods are supported. If a user passes an unsupported method (such as "PUT" or "DELETE"), it will default to "GET" and either return an unexpected result or throw a RestClientException. It would be better if they can give a more specific error message in this case, or support these additional Http Methods.