chore: Add probot-stale

https://probot.github.io/apps/stale/

There are a few years of stale issues and prs. This bot will close issues over a year old and give people a chance to respond if they think the issue should stay open. After a manual review of more recent issues, we should tighten this down to 60 or 90 days.

.github/stale.yml

@@ -0,0 +1,17 @@
+# Number of days of inactivity before an issue becomes stale
+daysUntilStale: 365
+# Number of days of inactivity before a stale issue is closed
+daysUntilClose: 7
+# Issues with these labels will never be considered stale
+exemptLabels:
+  - "Up for consideration"
+  - greenkeeper
+# 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