Support markdown comments #1149

Description:
It would be great to have markdown for the message for a stale PRs.
Justification:
This would allow for links and other basic markup to be added which could point to other resources the PR owner should look at to get their PR reviewed.

Are you willing to submit a PR?
Yes - I just want to check it's in scope before going through the effort 😅

Example

Figure: An example of the comments being considered text and not markdown, see SSWConsulting/SSW.GitHub.Template#24