added github stale issues bot

.github/stale.yml

+# Number of days of inactivity before an issue becomes stale
+daysUntilStale: 60
+# Number of days of inactivity before a stale issue is closed
+daysUntilClose: 14
+# Issues with these labels will never be considered stale
+exemptLabels:
+  - "T: Enhancement"
+  - "S: Triaged"
+# Label to use when marking an issue as stale
+staleLabel: "S: 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 in two weeks unless you comment.
+
+  Thank you for your contributions.
+# Comment to post when closing a stale issue. Set to `false` to disable
+closeComment: false