Introduce action to mark issues as stale

[kengu]

@johnpryan / @maRci002 / others: We have many issues with follow-up questions that are not answered by OP. Any thoughts on introduction action close-stale-issues to help us mark these as stale?

[johnpryan]

Sounds good to me - maybe 60 days is a good place to start?

[kengu]

Yes, I think that is a reasonable gracetime

[kengu]

An I think we should disable closing stale PRs with days-before-pr-close: -1

[kengu]

I don't have permissions to add this action though.

[johnpryan]

I see- yeah it would be nice to have a stale label automatically applied. I'll see if I can add this.