Describe the feature or problem you’d like to solve

PRs have a really nice way of leaving approvals, change requests, comments, and marking comments as resolved. gh cli does not appear to support comments on PRs

Proposed solution

CLI could allow commenting on a commit, filename, and line number, and it could allow retrieving all comments on all changes in a commit.

Additional context

This likely will need support from GH API -- There's comments on PR issues in general (https://developer.github.com/v4/object/pullrequest/) and comments for reviews: https://developer.github.com/v4/object/pullrequestreviewcomment/