Allow configuring the serialization context when using the request body converter

This PR adds the ability to configure the serialization context used by the request body converter:

```PHP
    /*
     * @ParamConverter("post", converter="fos_rest.request_body", options={"serializationContext"={"groups"={"group1"}, "version"="1.0"}})
     */
    public function postPostAction(Post $post)
    {
        // ...
    }
```