chore: close issues with no user response

[josxha]

• This pull request marks issues with the waiting for user response label automatically stale after 3 weeks. This is a reminder for the user to answer a question or provide requested information.
• After another week with no activity / user response, the issue gets closed automatically.
• If the user responds within the week the waiting for user response and stale label gets automatically removed.

[JaffaKetchup]

I have mixed feelings about this. We previously had this stale bot (admittedly without the tag exception rules), but it was a bit of a pain. Even if 50% of bug reports without enough information are invalid, that still leaves 50% that would be better investigated. Leaving them open allows other people to find issues and add their own info.
Would like some input from the others (@ibrierley, @TesteurManiak, @mootw).

[josxha]

(There is currently one problem with this PR: The waiting for user response will not get removed if the issue is not stale.)

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We previously had this stale bot (admittedly without the tag exception rules), but it was a bit of a pain.

I'm aware that this was used in the past. While it was configured to close all issues in the past, this pr gives automation for the waiting for user response label. It will only handle those and ignore all other issues.

Having some kind of automation around waiting for user response is required to ensure the label gets removed when it recieves an update. For my understanding waiting for user response is a useful label if an issue can't be reproduced or requires the answer to an question to be able to get solved.

#1760 is a good example what happens if we don't have this automation.

Even if 50% of bug reports without enough information are invalid, that still leaves 50% that would be better investigated.

It wouldn't make sense for us to tag those other 50% of valid bug reports with waiting for user response, therefore I can't see your argument here.

Leaving them open allows other people to find issues and add their own info.

It is still possible for other people to adopt such issues. As soon as an update gets posted the waiting for user response would get removed.

[JaffaKetchup]

Two minor changes to wording, let me know what you think of them.

[JaffaKetchup]

LGTM! Thanks :)

[josxha]

I tested the workflows on my fork, hope I fixed every bug.
Merging it.