github: add stalebot config

.github/stale.yml

@@ -0,0 +1,44 @@
+# Configuration for probot-stale: https://github.com/probot/stale
+
+# Limit the number of actions per hour, from 1-30. Default is 30
+limitPerRun: 30
+
+# Limit to only `issues` or `pulls`
+only: pulls
+
+# Number of days of inactivity before a PR becomes stale.
+daysUntilStale: 30
+
+# Number of days of inactivity before an Issue or Pull Request with the stale
+# label is closed.
+#
+# Set to false to disable. If disabled, issues still need to be closed manually,
+# but will remain marked as stale.
+daysUntilClose: 7
+
+# Only issues or PRs with all of these labels are checked if stale. Defaults to
+# `[]` (disabled).
+onlyLabels: []
+
+# Issues or Pull Requests with these labels will never be considered stale.
+# Set to `[]` to disable
+exemptLabels:
+  - "S:Pinned"
+
+# Set to true to ignore issues in a project (defaults to false)
+exemptProjects: false
+
+# Set to true to ignore issues in a milestone (defaults to false)
+exemptMilestones: false
+
+# Set to true to ignore issues with an assignee (defaults to false)
+exemptAssignees: false
+
+# Label to use when marking as stale
+staleLabel: "S:Stale"
+
+# Comment to post when marking as stale. Set to `false` to disable
+markComment: >
+  This PR 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.