Feature: Add an optional setting to only allow new contributors to take good first issues

[nickytonline]

Although it's always appreciated when people want to contribute to a project, for good first issues we really only want someone who's never contributed to the code base to be able to take those issues.

I'm proposing we add an option that is on by default that if the issue has the good first issue label, and the assignee has already had at least one issue assigned to them that we generate a comment like, "Thanks for your interest in this issue. It looks like this is a good first issue, and you've already contributed to the codebase. Let's leave this issue for a newcomer to the project."

Definitely would love some suggestions on the wording here @bekahhw @bdougie if we proceed with this issue.