[java-client][resteasy] use real PATCH instead of POST with "X-HTTP-Method-Override"

Created by: jmini

For PATCH call, the resteasy client should use a real "PATCH" method instead of using "POST" with "X-HTTP-Method-Override"

Example spec:

openapi: 3.0.1
info:
  title: OpenAPI Test
  description: Test Spec for a "Simple Client"
  version: 1.0.0
  license:
    name: Apache-2.0
    url: 'http://www.apache.org/licenses/LICENSE-2.0.html'
servers:
  - url: 'http://localhost:8090/'
paths:
  /pingPatch:
    patch:
      operationId: pingPatch
      responses:
        '201':
          description: OK

Code that must be changed:

https://github.com/OpenAPITools/openapi-generator/blob/10a310ef69d49742405b4b520b1d53b20b16e845/modules/openapi-generator/src/main/resources/Java/libraries/resteasy/ApiClient.mustache#L665-L666