[Bug][Java][Spring] Missing description with Swagger2 annotations

I've noticed an issue when generating code using the Java Spring generator regarding the description when using Swagger2 annotations, i.e. the default option. The description is added to the JavaDoc, but not to the @Operation annotation.

The issue can be reproduced with 5.4.0, 6.0.0 and master.

• 5.4.0 lacks the description parameter at all
• 6.0.0 adds it, but it doesn't change anything

It's pretty simple to reproduce this issue. Here is a small example illustrating the issue:

paths:
  /path:
    get:
      summary: Some short text
      description: Some long text
      responses:
        200:
          description: OK

This generates to the following (snip):

/**
    * GET /path : Some short text
    * Some long text
    *
    * @return OK (status code 200)
    */
@Operation(
    summary = "Some short text",
    responses = {
        @ApiResponse(responseCode = "200", description = "OK")
    }
)
@RequestMapping(
    method = RequestMethod.GET,
    value = "/path",
    consumes = { "application/json" }
)
default ResponseEntity<Void> someMethod() {
    return new ResponseEntity<>(HttpStatus.NOT_IMPLEMENTED);
}

As you can see, it lacks the description within the @Operation annotation.

There is no special configuration needed, just use the defaults: generate -i test.yaml -g spring -o testgen

As far as I've understood to me it looks like there is a mismatch between the api.mustache file and Codegen structure. For the JavaDoc the template file uses notes, but for the description it tries to use description. As far as I can see in the DefaultCodegen#fromOperation only notes are set and therefore description is always empty/null/non-existing.

Start with the Spring generator's api.mustache template and DefaultCodegen#fromOperation, where the issue reports that only notes is populated. Reproduce the behavior with generate -i test.yaml -g spring -o testgen using the supplied OpenAPI example. Done means the generated @Operation annotation includes the path description, while the existing JavaDoc and response description remain correct.