[BUG][JAVA][MAVEN] Avoid Mono<T> wrapper around method parameters

Bug Report Checklist

• Have you provided a full/minimal spec to reproduce the issue?
• Have you validated the input using an OpenAPI validator (example)?
• Have you tested with the latest master to confirm the issue still exists?
• Have you searched for related issues/PRs?
• What's the actual output vs expected output?
• [Optional] Sponsorship to speed up the bug fix or feature request (example)

Description

Generating an interface using reactive flag, and an open-api.yaml like this:

/sample-patch:
    patch:
      summary: Sample Update.
      tags:
        - userDevices
      operationId: sampleUpdate
      requestBody:
        content:
          application/json:
            schema:
              $ref: '#/components/schemas/SamplePatchRequest'
        required: true

Generates a method like this

default Mono<ResponseEntity<String>> sampleTest(Mono<SamplePatchRequest> samplePatchRequest, ServerWebExchange exchange) {
    Mono<Void> result = Mono.empty();
    exchange.getResponse().setStatusCode(HttpStatus.NOT_IMPLEMENTED);
    Iterator var5 = exchange.getRequest().getHeaders().getAccept().iterator();

    while(var5.hasNext()) {
        MediaType mediaType = (MediaType)var5.next();
        if (mediaType.isCompatibleWith(MediaType.valueOf("application/json"))) {
            String exampleString = "{ \"createdAt\" : \"2000-01-23\", \"active\" : true }";
            result = ApiUtil.getExampleResponse(exchange, exampleString);
            break;
        }
    }

    return result.then(Mono.empty());
}

The desired result was to receive the same result without mono wrapper

    default Mono<ResponseEntity<String>> sampleTest(SamplePatchRequest samplePatchRequest, ServerWebExchange exchange){
    Mono<Void> result = Mono.empty();
    exchange.getResponse().setStatusCode(HttpStatus.NOT_IMPLEMENTED);
    Iterator var5 = exchange.getRequest().getHeaders().getAccept().iterator();

    while(var5.hasNext()) {
        MediaType mediaType = (MediaType)var5.next();
        if (mediaType.isCompatibleWith(MediaType.valueOf("application/json"))) {
            String exampleString = "{ \"createdAt\" : \"2000-01-23\", \"active\" : true }";
            result = ApiUtil.getExampleResponse(exchange, exampleString);
            break;
        }
    }

    return result.then(Mono.empty());
}

Suggest a fix

I updated my open-api-template/bodyParams.mustache and open-api-template/apiDelegate.mustache file, in order to fix autogenerated code. It could be considered a valid solution to apply? (files in attachments)
open-api-template.zip

Reproduce the issue with the provided OpenAPI YAML and reactive setting, then inspect open-api-template/bodyParams.mustache and open-api-template/apiDelegate.mustache. Compare the generated interface signature with the requested output; done means method parameters no longer use the Mono wrapper while the reactive return type remains.