Add stale-bot configuration.

[jordandrako]

Description of changes

Add configuration for Stale bot https://github.com/apps/stale
Stale is a GitHub Integration built with Probot that closes abandoned issues after a period of inactivity.

Will require repo admin to install the integration such as @dzearing.

Proposed configuration:

• Mark as stale after 30 days of inactivity.
• If no activity after marking as stale, close after 14 more days.
• Exempt following labels from being marked as stale
  • Priority 0
  • Priority 1
  • Needs: discussion
  • Needs: revisit
• Stale bot adds no-recent-activity tag on stale issues
• Stale bot comments on marking stale: "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 to Fabric React!"
• Stale bot comments on closing: "This issue has been automatically closed because it has not had recent activity after being marked as stale. If you belive this issue is still a problem or should be reopened, please reopen it! Thank you for your contributions to Fabric React!"
• Will do this in batches of 30 per hour to prevent spamming too much.
• Limit bot to only running on issues, not on pull requests for now.