Build tooling: Add stale-bot action

[vanessayuenn]

What I did

Adding back stale bot but a lot more scoped down:

• The bot will only process issues labeled needs reproduction or needs more info
• Issues labeled as needs triage are always exempted
• The bot will mark issues stale if no response in 21 days
• When there is a response, the label needs triage is added back
• Caveat: We need to proactively remove needs repro label, if a repro is provided within 21 days after needs reproduction label is added. Otherwise, the issue will still be marked as stale if there is no activity for 21 days.

Checklist

• Make sure your changes are tested (stories and/or unit, integration, or end-to-end tests)
• Make sure to add/update documentation regarding your changes
• If you are deprecating/removing a feature, make sure to update
  MIGRATION.MD

Maintainers

• If this PR should be tested against many or all sandboxes,
  make sure to add the ci:merged or ci:daily GH label to it.
• Make sure this PR contains one of the labels below.

["cleanup", "BREAKING CHANGE", "feature request", "bug", "documentation", "maintenance", "dependencies", "other"]

[shilman]

Looks great!