Clean up stale issues and pull requests

[MHarris021]

What is the goal / desired outcome?

The goal is to mark issues and pull requests as stale if they haven't been actively worked on or updated within 180 days. <-- Open to smaller number here. If the issues or pull requests continue to not be worked or updated after being labeled stale then automatically close them. Cleaning up stale issues and pull requests will make it easier to determine current roadmap and will reduce complexity for new developers approaching the project.

(Optional) What is your proposal for a feature to solve this?

I propose using Github actions to implement this feature as there exist several ways of doing this already.

[JoeyZwicker]

We had a version of this a long while ago and perhaps we made it too aggressive. All said, yes we want to be better about keeping GH clean. cc @BOsterbuhr to our previous conversation about improving GH transparency further.