PROBLEM
right now our bot-inactivity-unassign bot is working nicely to unassign users to issues that have been assigned an issue, but do not have a PR.

However, we also need to unassign users that show inactivity within pull requests.

SOLUTION
Expand bot-inactivity-unassign bot to automatically unassign users from issues if their tied OPEN PULL REQUEST has no COMMIT activity for at least 21 days. It should also close this open pull request that is stale.

Perhaps this can be tied to a second .sh script if we believe they are like separate things

NOTES
It should provide a helpful message once they are unassigned.
E.g.
"Hi, this is InactivityBot.
This pull request has become stale, with no development activity for 21 days. As a result, we have closed this pull request and unassigned you from the issue.
You are welcome to get assigned to an issue once again once you have capacity
In the future, please close old pull requests that will not have development activity and request to be unassigned if you are no longer working on the issue"
or similar