[JavaSpring] Allow configuring generic ResponseEntity for Spring generator.

[zamzterz]

Add configuration option generateGenericResponseEntity for Spring generator to allow generating generic ResponseEntity<?> controller-method return type.

Fixes #1096, fixes #17520

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[wing328]

did a test and here is the change using the example spec mentioned in the issue

 @Validated
 @Tag(name = "example", description = "the example API")
 public interface ExampleApi {
@@ -67,7 +67,7 @@ public interface ExampleApi {
         produces = { "application/json" }
     )

-    default ResponseEntity<Object> examples(
+    default ResponseEntity<?> examples(

     ) {
         getRequest().ifPresent(request -> {

[wing328]

thanks for the PR

let's give it a try