Don't add the comment if it already exists

Rather than requiring regex to delete comments, it would be great if this would automatically check if the comment exists, and if so, do not add a further comment.

For example, when setting up a PR review environment, we don't want it to constantly post the URL to the PR. We only need it done once.

Start by locating the command path that creates comments for pull requests, reviews, issues, or commits and trace its GitHub API calls. Check how existing comments can be identified, then verify that rerunning the command leaves an existing matching comment unchanged while still adding a missing one.

Written by the indexing model from the issue text.