feat: add auto merge information to pull request

[jeskosda]

Description

Hey ✋🏻 , as already clarified in #1245, this PR will add the auto merge object to the GHPullRequest.

Closes #1245

auto_merge:
      title: Auto merge
      description: The status of auto merging a pull request.
      type: object
      properties:
        enabled_by:
          "$ref": "#/components/schemas/simple-user"
        merge_method:
          type: string
          description: The merge method to use.
          enum:
            - merge
            - squash
            - rebase
        commit_title:
          type: string
          description: Title for the merge commit message.
        commit_message:
          type: string
          description: Commit message for the merge commit.
      required:
        - enabled_by
        - merge_method
        - commit_title
        - commit_message
      nullable: true

The structure is double-checked against a request against the /pulls API:

{
...,
"auto_merge": {
    "enabled_by": {
      "login": "jeskosda",
      "id": 1,
      "node_id": "xxx",
      "avatar_url": "https://avatars.githubusercontent.com/u/61695677?v=4",
      "gravatar_id": "",
      "url": "https://api.github.com/users/jeskosda",
      "html_url": "https://github.com/jeskosda",
      "followers_url": "https://api.github.com/users/jeskosda/followers",
      "following_url": "https://api.github.com/users/jeskosda/following{/other_user}",
      "gists_url": "https://api.github.com/users/jeskosda/gists{/gist_id}",
      "starred_url": "https://api.github.com/users/jeskosda/starred{/owner}{/repo}",
      "subscriptions_url": "https://api.github.com/users/jeskosda/subscriptions",
      "organizations_url": "https://api.github.com/users/jeskosda/orgs",
      "repos_url": "https://api.github.com/users/jeskosda/repos",
      "events_url": "https://api.github.com/users/jeskosda/events{/privacy}",
      "received_events_url": "https://api.github.com/users/jeskosda/received_events",
      "type": "User",
      "site_admin": false
    },
    "merge_method": "squash",
    "commit_title": "Test",
    "commit_message": "Test"
  }
}

[codecov]

Codecov Report

Merging #1247 (1b5de5b) into main (b92c060) will increase coverage by 0.04%.
The diff coverage is 100.00%.

@@             Coverage Diff              @@
##               main    #1247      +/-   ##
============================================
+ Coverage     77.42%   77.47%   +0.04%     
- Complexity     1899     1901       +2     
============================================
  Files           189      189              
  Lines          5972     5985      +13     
  Branches        327      327              
============================================
+ Hits           4624     4637      +13     
  Misses         1150     1150              
  Partials        198      198              

Impacted Files	Coverage Δ
...rc/main/java/org/kohsuke/github/GHPullRequest.java	77.86% <100.00%> (+1.06%)	⬆️
src/main/java/org/kohsuke/github/GHRepository.java	68.42% <0.00%> (+0.34%)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update b92c060...1b5de5b. Read the comment docs.