Remove pending builds from the queue when builds can not be processed

Problem

As brought up by @grzesiek when working on denormalizing shared runners information to ci_pending_builds :

I think that this iteration might not be complete if we do not update pending builds whenever builds get disabled or a project gets removed, or shared runners get disabled (like in case of the CI minutes where we need to update ci_pending_builds when someone purchases new minutes). We can implement that in a separate merge request if you feel that this would be desirable.

This will make sure we ensure data consistency when using our new queuing mechanism.

Solution

Option 1

We need to update ci_pending_builds#instance_runners_enabled when:

• Projects get removed
• Builds get disabled for the project
• Shared runners are getting disabled / enabled in a project or a group

Do no queue not active builds

Not applicable

We could leverage our existing prerequisite abstraction which runs some business logic before transition a build as pending.

This has the advantage of not dealing with more denormalization data to ci_pending_builds and not having to deal with data integrity issues.

cc @grzesiek