Delegate stalebot config to org-level file

See edgi-govdata-archiving/overview#235

Author: Mr0grog

.github/stale.yml

@@ -1,18 +1 @@
-# Number of days of inactivity before an issue becomes stale
-daysUntilStale: 180
-# Number of days of inactivity before a stale issue is closed
-daysUntilClose: 7
-# Issues with these labels will never be considered stale
-exemptLabels:
-  - never-stale
-  - security
-  - bug
-# 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 in seven days if no further activity occurs. If it should not be closed, please comment! Thank you
-  for your contributions.
-# Comment to post when closing a stale issue. Set to `false` to disable
-closeComment: false
+_extends: .github