Add more field to NoteEvent.ObjectAttributes

[yuezhuangshi]

This pull request adds more field to NoteEvent.ObjectAttributes

Currently, the data structure of NoteEvent.ObjectAttributes is consistent with the offical document , but after testing, I found that the actual data structure of NoteEvent.ObjectAttributes has more field, and I need discussion_id and type field for custom purposes.

"object_attributes": {
    "attachment": null,
    "author_id": 1234,
    "change_position": null,
    "commit_id": null,
    "created_at": "2021-03-16 16:39:18 UTC",
    "discussion_id": "56e2b4210419aed077d47ca2dc00551c7c4ac882",
    "id": 351809,
    "line_code": null,
    "note": "/tbd 12321 12321",
    "noteable_id": 2344,
    "noteable_type": "Issue",
    "original_position": null,
    "position": null,
    "project_id": 2072,
    "resolved_at": null,
    "resolved_by_id": null,
    "resolved_by_push": null,
    "st_diff": null,
    "system": false,
    "type": "DiscussionNote",
    "updated_at": "2021-03-16 16:39:18 UTC",
    "updated_by_id": null,
    "description": "/tbd 12321 12321",
    "url": "http://xx.xx.xx.xx/xyxy/abc/issues/1#note_351809"
  }

[yuezhuangshi]

@jabby Cloud you please review this PR and release a version ASAP?

[jabby]

@yuezhuangshi Thanks for your PR. I will review it for the 4.16 milestone. No release date defined yet. There is no snapshot build either actually but are you interested in a 4.16-snapshot? If so, I will create a snapshot really soon.

[yuezhuangshi]

@jabby Can you release a version gitlab4j-api-4.15.8 with this PR?