cicd: update stalebot

[korikuzma]

• create reusable workflow (it might make sense to make other actions as reusable workflows)
• add stale actions for high/medium/low priority labels

[jsstevenson]

@korikuzma Does this make bug also stale-exempt?

[korikuzma]

@korikuzma Does this make bug also stale-exempt?

@jsstevenson Not for this repo. I just used the default label stale-exempt. When other repos use the reusable-stale.yaml, they can have a job that specifies exempt labels and that can include bug if needed. However, I'm kind of hesitant about marking too many issues as stale exempt because it might reduce the effectiveness of stalebot. Sometimes issues labeled as bug have been completed, but have not been closed. So I think stale-exempt labels to be used sparingly. Open to other people's thoughts on this.

[korikuzma]

Another comment is for repos that have many issues without priority labels, we might want something like:

  stale-no-priority-labels:
    uses: ./.github/workflows/reusable-stale.yaml
    with:
      days-before-issue-stale: 90
      days-before-pr-stale: 7
      exempt-labels: stale-exempt,priority:low,priority:medium,priority:high