Add support for file comments in PRs

[camillof]

Resolves #1710

---

Before the change?

• Even if you provided a nil line when creating a pull request comment, with the intention of commenting the whole file, you would get an answer like

{
  "message": "Invalid request.\n\nNo subschema in \"oneOf\" matched.\n\"position\" wasn't supplied.\n\"in_reply_to\" wasn't supplied.\n\"subject_type\" is not a permitted key.\nFor 'properties/line', nil is not an integer.\n\"line\" is not a permitted key.",
  "documentation_url": "https://docs.github.com/rest/pulls/comments#create-a-review-comment-for-a-pull-request",
  "status": "422"
}

Per GitHub documentation:

line integer
Required unless using subject_type:file. ...

After the change?

• If you don't provide a line, the file subject type will be used, allowing users to create file comments.

client.create_pull_request_comment(repo, pr_number, body, commit, path)

Pull request checklist

• Tests for the changes have been added (for bug fixes / features)
• Docs have been reviewed and added / updated if needed (for bug fixes / features)

Does this introduce a breaking change?

Please see our docs on breaking changes to help!

• Yes
• No

---

[github-actions]

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[kfcampbell]

This seems reasonable. Thanks for the change!