Add auto-handling of stale PRs/Issues (#7197)

Add auto-handling of stale PRs/Issues (#7197)

* Add auto-handling of stale PRs/Issues

This adds the configuration for probot-stale, so that PRs and Issues can be automatically pruned without intervention by collaborators.

This marks PRs with `awaiting changes` label after 45 days, and then closes any PR with "Awaiting changes" after 30 days.  Unless they have `awaiting review`, `breaking_changes`, `in progress` or `on hold` labels.

This marks issues as `solved` after 90 days, and then closes them 30 days afterwards. Unless they have `bug`, `discussion, `to do`, `in progress` or `on hold` labels.

* Cleanup the text some

* Update .github/stale.yml

Co-Authored-By: fauxpark <fauxpark@gmail.com>