Provide a better way to clean up stale builds

Problem Definition

In some scenarios, builds can get stuck in the queue and, if concurrent builds are not allowed, new builds for the same plan can not be executed. Currently, the only way to mitigate this problem is by restarting the Bamboo service.

Suggested Solution

It would be nice if we have a way to do that without causing downtime.

Workaround

The current workaround for this problem is to restart the application.