Add probot/stale config

.github/stale.yml

@@ -0,0 +1,15 @@
+# Issues/PRs with no activity for a year will be marked as stale
+daysUntilStale: 365
+
+# If no one has replied inside a week after an issue is marked stale, close it.
+daysUntilClose: 7
+
+staleLabel: wontfix
+markComment: >
+  This issue or PR has been automatically marked as stale because there has been
+  no activity in over a year. It will be closed in 1 week if no further activity occurs.
+  Thanks for your contribution, and please don't hesitate to comment if this issue/PR
+  is still relevant.
+exemptLabels:
+  - pinned
+  - security