Encoding section for multipart requests do not work

[patrykpacewicz]

Describe the bug
swagger.io documentation has support for adding your own Content-Type for specific parts of multipart / form-data request and springdoc also has this support, but when it's set, it doesn't appear in the result JSON

• https://swagger.io/docs/specification/describing-request-body/multipart-requests/#content-type

To Reproduce

@RestController
public class HelloController {

    @PostMapping(value = "/test/103", consumes = MediaType.MULTIPART_FORM_DATA_VALUE)
    @Operation(
            requestBody = @RequestBody(content = @Content(encoding = @Encoding(name = "body", contentType = "application/json")))
    )
    public String postMyRequestBody(
            @RequestPart("body") ExampleBody body,
            @RequestParam("file") MultipartFile file
    ) { return null; }
}

Expected behavior
In the JSON response, we should see additional section

"encoding":{ "body":{ "contentType":"application/json" } }