meta: merge stalebot and update timings/messages

This PR will consolidate the feature-request and pull request stalebots into a unified workflow that targets all issues and all pull requests.

Focusing solely on feature-request issues seems unnecessary, as other issues can also become stale.

Instead of relying on @mhdawson's fork, which has been great, this PR will update the stale-bot to the latest version (v9.0.0).

However, there's a trade-off. Without the fork, the stalebot loses the endDate controlling environment variable. To address this, I've set the stale timeout to a middle ground between the endDate and the stale timeout (8 months).

Previously, the check was for issues older than a year with no updates in the past 6 months. Now, it will check for issues without any updates in 8 months. The middle ground would technically be 9 months, but I think 8 months strikes a good balance in this case.