Add Stale configuration (#14109)

Similar to openhab/openhab-core#2974

See also: https://github.com/marketplace/stale

Signed-off-by: Wouter Born <github@maindrain.net>

.github/stale.yml

@@ -0,0 +1,23 @@
+# Number of days of inactivity before an issue becomes stale (two month)
+daysUntilStale: 60
+# Number of days of inactivity before a stale issue is closed (another six month)
+daysUntilClose: 180
+# Issues with these labels will never be considered stale
+exemptLabels:
+  - pinned
+  - security
+  - "PR pending"
+# Only issues with all of these labels are checked if stale.
+onlyLabels:
+  - "awaiting feedback"
+# 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
+# Limit to only `issues``
+only: issues