feature: add stale pr workflow

Signed-off-by: Terry Howe <terrylhowe@gmail.com>

.github/workflows/stale.yaml

@@ -11,6 +11,7 @@ jobs:
       with:
         repo-token: ${{ secrets.GITHUB_TOKEN }}
         stale-issue-message: 'This issue has been marked as stale because it has been open for 90 days with no activity. This thread will be automatically closed in 30 days if no further activity occurs.'
+        stale-pr-message: 'This pull request has been marked as stale because it has been open for 90 days with no activity. This pull request will be automatically closed in 30 days if no further activity occurs.'
         exempt-issue-labels: 'keep open,v4.x,in progress'
         days-before-stale: 90
         days-before-close: 30