Convert GitLab's pr comments to the domain layer

[Startrekzky]

Describe the solution you'd like

• Convert Gitlab MR comments to the domain layer's pull_request_comments

Belongs to

#1746

[klesh]

Actual: pr_comments in Gitlab was named GitlabMergeRequestNote, and converted to Note
Expected: GitlabMergeRequestNote to be converted to PullRequestComments

[warren830]

Actual: pr_comments in Gitlab was named GitlabMergeRequestNote, and converted to Note Expected: GitlabMergeRequestNote to be converted to PullRequestComments

This has been done before: