.github: Add workflow to stale pull requests (#51237)

Summary:
Pull Request resolved: #51237

Stales pull requests at 150 days and then will close them at 180 days

Signed-off-by: Eli Uriegas <eliuriegas@fb.com>

Test Plan: stonks

Reviewed By: yns88

Differential Revision: D26112086

Pulled By: seemethere

fbshipit-source-id: c6b3865aa5cde3415b6dd6622c308895a16e805f

.github/workflows/stale_pull_requests.yml

@@ -0,0 +1,34 @@
+name: 'Close stale pull requests'
+on:
+  schedule:
+    - cron: '30 1 * * *'
+  workflow_dispatch:
+
+jobs:
+  stale:
+    if: ${{ github.repository_owner == 'pytorch' }}
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/stale@v3
+        with:
+          stale-pr-message: >
+            Looks like this PR hasn't been updated in a while! Going to go ahead and mark this as `stale`.
+            Feel free to update / remove the `stale` label if you feel this is a mistake
+            `stale` pull requests will automatically be closed 30 days after being marked `stale`
+          exempt-pr-labels: "no-stale,open source,high priority"
+          days-before-stale: 60
+          days-before-close: 90
+  stale-open-source:
+    if: ${{ github.repository_owner == 'pytorch' }}
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/stale@v3
+        with:
+          stale-pr-message: >
+            Looks like this PR hasn't been updated in a while! Going to go ahead and mark this as `stale`.
+            Feel free to update / remove the `stale` label if you feel this is a mistake
+            `stale` pull requests will automatically be closed 30 days after being marked `stale`
+          exempt-pr-labels: "no-stale,high priority"
+          only-labels: "open source"
+          days-before-stale: 150
+          days-before-close: 180