Add some automation to help manage GitHub issues

[bartekpacia]

Automate triage process a bit.

Proposed Changes

Add 2 new periodic scheduled GitHub Actions workflows:

• close-inactive-issues - close issues that have had the "waiting for customer response" label for too long (configurable)

• lock-closed-issues - lock issues that have been closed for long enough (configurable). to prevent people from "reviving" old issue from the graveyard. There are no downsides to creating a new issue with up-to-date info and referencing the old, closed one.

Generally, the new triage workflow I propose is:

1. Open a new issue, read through it, make sure it is reproducible, or at least we know what's happening
2. If it's not reproducible/we don't know what's happening, ask for more information and assign the waiting for customer response label
3. When the user/customer responds and we're satisfied with information, remove the waiting for customer response label (and possibly add new appropriate labels)

If the customer doesn't respond within some timeframe, their issue will get closed, and then locked.

This process is based on Flutter's triage process (I think they got it sorted really well - they have to, they're huge).

Notes

• All existing closed issues will be locked. This may be big, we may not want it. We can wait with this change. I want feedback.

• None of the existing issues will be closed. We don't want to close any issues unless we're sure they're invalid/outdated etc. In other words, this will only apply to issues that will have the waiting for customer response label – which is 0 now.

Testing

This workflow is basically copy-pasted from the Flutter project, where it has been working well for years.

Issues Fixed

n/a