Issue label automation and stale issue checker

[mason-at-pieces]

Ok so I added 2 workflows:

1. The label-updater workflow handles the following:
   • When a Pieces team member responds to an issue with the "status:needs triage" label, we can remove that label and add the "waiting on user response" label.
   • If the author responds, we can remove the "status:waiting on user response" and add a "status:user responded" label
2. The stale-issue-checker runs once a day and the workflow handles the following:
   • Sends a nudge after 3 days of inactivity if it has the "waiting on user response" label
   • Automatically closes the issue due to inactivity after 7 days if it has the "status:waiting on user response" label