Webhook (or other alerts) when a build has been clogging up the queue

[charliegroll]

Problem

Some of our build checks will be pending until someone takes action (approving visual regression snapshot changes, for example). With kodiak, most people tend to "set it to merge and forget it."

Proposed solution

Set a configurable threshold time that publishes to a webhook after that time has passed to notify that the queue is blocked (and maybe repeat the check X times as a reminder?). My team could subscribe to this in Slack (or PagerDuty, or email, etc) so we can unblock our queue before it backs up too much.