Integrate stale application to EvalAI repository

.github/stale.yml

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+# Number of days of inactivity before an Issue or Pull Request becomes stale
+daysUntilStale: 60
+
+# 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
+
+# Issues or Pull Requests with these labels will never be considered stale. Set to `[]` to disable
+exemptLabels:
+  - priority-high
+  - critical
+
+# Label to use when marking as stale
+staleLabel: inactivity
+
+issues:
+  # Comment to post on issues when marking 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.
+  closeComment: >
+    This issue has been automatically closed as there is no further activity. Thank you
+    for your contributions.
+
+pulls:
+  # Comment to post on pull requests when marking as stale. Set to `false` to disable
+  markComment: >
+    This pull request 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 Pull Request.
+  closeComment: >
+    This pull request has been automatically closed as there is no further activity. Thank you
+    for your contributions.