gha: create stale issue workflow

[rockwotj]

A Github action to mark all bug reports that haven't had activity in 3 months as stale. Stale issues are closed after 2 weeks. This is setup using https://github.com/actions/stale

Backports Required

• none - not a bug fix
• none - this is a backport
• none - issue does not exist in previous branches
• none - papercut/not impactful enough to backport
• v23.3.x
• v23.2.x
• v23.1.x

Release Notes

• none

[ivotron]

this is related: https://github.com/redpanda-data/devprod/issues/668. There wasn't a conclusion from the associated discussion (slack thread), specially regarding doing a first pass to avoid closing everything that's currently 90 days old, did that get resolved? I think the idea, in the context of this PR, was to have a first pass and mark preserve to anything that we want to preserve currently

[rockwotj]

There is some discussion internally on what to do with older issues. This action has the ability to only process stuff after a specific date, so we can use that to not mark old stuff.

@mattschumpert and @piyushredpanda had thoughts here