chore: Add Stale Bot config (OHIF#802)

.github/stale.yml

@@ -0,0 +1,26 @@
+# GitHub App: Stale
+# https://github.com/apps/stale
+#
+# Number of days of inactivity before an issue becomes stale
+daysUntilStale: 21
+# Number of days of inactivity before a stale issue is closed
+daysUntilClose: 7
+# Issues with these labels will never be considered stale
+exemptLabels:
+  - 'Story 🙌'
+  - 'Bug: Verified 🐛'
+  - 'Task: CI/Tooling 🤖'
+  - 'Task: Docs 📖'
+  - 'Task: Refactor 🛠'
+  - 'Task: Tests 🔬'
+  - 'Triage 🏳️'
+  - 'Announcement 🎉'
+# Label to use when marking an issue as stale
+staleLabel: 'Stale 🥖'
+# Comment to post when marking an issue as stale. Set to `false` to disable
+markComment: >
+  This issue has been automatically marked as stale because it has not had
+  recent activity. It will be closed if no further activity occurs. Thank you
+  for your contributions.
+# Comment to post when closing a stale issue. Set to `false` to disable
+closeComment: false