[REQ] [JavaSpring] Header based API operation versioning

Is your feature request related to a problem? Please describe.

We would like version the behavior of an API operation, for which the desired distinction was decided to be sent via
an API header, but the latest server generator does not generate the header parameter for the RequestMapping annotation, thus
Spring cannot distinguish between the different version implementations.

...
    @Operation(
        operationId = "getSomeTag",
        tags = { "SomeTag" },
        responses = {
            @ApiResponse(responseCode = "200", description = "OK")
        }
    )
    @RequestMapping(
        method = RequestMethod.GET,
        value = "/some/dummy/endpoint",

this does not get generated into the class -->        headers = { "v2HeaderParam" }

    )
    default ResponseEntity<SomeTagV2> getSomeTagV2(...)
...
    @Operation(
        operationId = "getSomeTag",
        tags = { "SomeTag" },
        responses = {
            @ApiResponse(responseCode = "200", description = "OK")
        }
    )
    @RequestMapping(
        method = RequestMethod.GET,
        value = "/some/dummy/endpoint"
    )
    default ResponseEntity<SomeTag> getSomeTag(...)
...

Describe the solution you'd like

Change the Api.mustache template to include required header parameters into the RequestMappings annotation.
To achieve this the CodegenOperationModel members have to be aligned to contain the required headers too (currently there are only members for headers and required parameters, which are not eligible for the template controls).

Describe alternatives you've considered

Using Api versioning or a different resource is for some use cases not an option.

Additional context

N/A

Start by locating the Api.mustache template and the CodegenOperationModel members used by its template controls. Trace how header parameters and required parameters reach the JavaSpring generator, then verify that required headers appear in generated RequestMapping annotations so versioned operations can be distinguished.