Allow to pass additional context to pr-auditor exceptions

Created by: jhchabran

In the sec-pr-audit-trail ticket it would be great if we could inform the user that they now need to also merge their changes into preprod as well otherwise the next automated release will be stuck waiting for someone to click Update Branch or merge release -> preprod again.

Originally posted by @danieldides in https://github.com/sourcegraph/sourcegraph/issues/33959#issuecomment-1100140750