Opting in to stale botting

[hyandell]

[I've not used the action, but this came up in conversation and I was encouraged to share the thought]

Stale botting issues/PRs seems to be a potential for unhappiness. It can often come across as harsh to the opener of the issue/PR.

I've seen stalebots where you can opt an issue/PR out of the staling; but my thought is that issues should need to be opted in to be stale botted. The project owner would be responsible for the first review of an issue/PR, and they would decide to add a label of 'canstale' to allow the stablebot to show up.

They would be triaging it the issue as "not critical", and possibly also identifying the next step. It's akin to making it "Pending Community - Close in 90 days".