chore(stale.yml): Auto manager for stale issues.

This will ensure that non-issues are closed after 90 days of inactivity.

.github/stale.yml

@@ -0,0 +1,20 @@
+# Number of days of inactivity before an issue becomes stale
+daysUntilStale: 60
+# Number of days of inactivity before a stale issue is closed
+daysUntilClose: 30
+# Issues with these labels will never be considered stale
+exemptLabels:
+  - help wanted
+  - good first issue
+# 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: >
+  This issue has been automatically closed because it has not had recent activity.
+  If you believe that this is still an issue in the latest version, feel free to re-open it.
+  Thank you for your contributions.