chore: Add stalebot configuration (#134)

.github/stale.yml

@@ -0,0 +1,21 @@
+# Number of days of inactivity before an issue becomes stale
+daysUntilStale: 30
+
+# Number of days of inactivity before a stale issue is closed
+daysUntilClose: 7
+
+# Issues or Pull Requests with these labels will never be considered stale. Set to `[]` to disable
+exemptLabels:
+  - enhancement
+  - dontstale
+
+# 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 been updated in the last 30 days. It will be closed if no further activity occurs within the next 7 days. Feel free to reach out or mention Box SDK team member for further help and resources if they are needed.
+
+# Comment to post when closing a stale issue. Set to `false` to disable
+closeComment: >
+  This issue has been automatically closed due to maximum period of being stale. Thank you for your contribution to Box iOS Preview SDK and feel free to open another PR/issue at any time.