Policy bot UI doesn't handle repository moves

[ajlake]

Repro:

• Have a repository at ORG1/REPO
• Open pull request against ORG1/REPO (policy-bot will post a status with a link to the UI, the UI link will be DOMAIN/details/ORG1/REPO/ISSUENO)
• Move the repository from ORG1 to ORG2
• The previous link will now be broken and the bot will return errors like the following: {"error":"Internal Server Error","request_id":"c9a6jc2nrpqc07dvlidg"}

Desired:

• Ideal: policy-bot should handle repository moves and follow redirects OR post an updated status check on repository move (assuming this is a detectable event)
• Better than nothing: instead of an opaque error, a message is displayed to the user with something like "Repository not found, possible causes: $LIST"

Note: this is a very minor edge issue and is resolved on the next status check posted from the bot.