ci: add workflow to close stale issues

[maschad]

Closes #2203

Introduces a workflow to clean up potentially stale issues / bugs raised where we need author input to progress.

This workflow requires two new labels awaiting and stale

So the sequence of actions would be this:

1. A user (whether code owner or not) creates an issue, no label is assigned to it.
2. A code owner responds to that issue, but determines that more information is needed to proceed, they assign the awaiting label
3. Only one that awaiting label has been assigned to the issue, the countdown (of 14 days in this case) begins, after 14 days the label stale is assigned to the issue and a generated warning is commented by the github bot that the issue will close in 7 days
4. After 7 days of the issue being stale it is closed by the github bot.

[arboleya]

Thanks for the PR and adjustments! 🙌

[Torres-ssf]

🚀

[github-actions]

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