`interruptible` does not cancel child pipelines

Problem

From #32837 (comment 293246134)

when using Parent/Child pipelines, interruptible doesn't cancel the child pipeline jobs. It only cancels the parent trigger job and leave the child pipeline running.

The same issue occurs when canceling the parent pipeline from the UI, parent pipeline cancels however child remains running.

Solution

We should also cancel the "interruptible" jobs of child pipelines when a new commit arrives in the same branch.

Technical note

• Now, CancelPendingPipelines looks for the pipelines that are only from ci_sources.
• We need to modify auto_cancelable_pipelines to include child pipelines.