stale bot: tune up a little

[blaggacao]

180 days is quite a large threshold to indicate that an issue or PR is stale
As the authors of the stalebot put it:

To some, a robot trying to close stale issues may seem inhospitable or offensive to contributors. But the alternative is to disrespect them by setting false expectations and implicitly ignoring their work. This app makes it explicit: if work is not progressing, then it's stale. A comment is all it takes to keep the conversation alive.

So what is stale? A conversation where nobody is interacting for 60 or 90 days, probably anyone would agree it's is stale.

Let's remember: un-staleing just needs a comment.

Motivation for this change

https://github.com/probot/stale#is-closing-stale-issues-really-a-good-idea

[zowoq]

180 days is quite a large threshold to indicate that an issue or PR is stale

This was discussed in NixOS/rfcs#51.

As there was so much discussion about the 180 day timeout in the RFC I don't really see it being changed without an RFC amendment.

[blaggacao]

Can't we just experiment for a while, and if there is bad feedback, roll it back? @ryantm please feel entitled to make the final call, if this can't proceed within reasonable effort, rather let's close this.

@zowoq I think the accepted formulation makes it almost explicit to open for experiment:

Start by using the following .github/stale.yml configurationfile:

(bold not in original text)

[ryantm]

@blaggacao It was pretty clear to me from the RFC feedback that it was only accepted because of the long period before things were marked stale, so I agree with @zowoq that we'd need an RFC amendment to make this change.

[blaggacao]

@ryantm Ok, if that's needed, I can go ahead and pull something together quickly in the style of https://github.com/NixOS/rfcs/blob/master/rfcs/0071-retired-committers-amendment.md If you don't oppose, I'll put you as co-author, agreed?

[ryantm]

@blaggacao I don't think the ROI of the effort is high enough, so I'd prefer to not be a co-author.

[ryantm]

Let's close this until the RFC is finished.