[feature request] Support Auto Cancellation

[gaocegege]

Is this a BUG REPORT or FEATURE REQUEST?:

/kind feature

Auto Cancellation allows you to only run builds for the latest commits in the queue. This setting can be applied to builds for Branch builds and Pull Request builds separately. Builds will only be cancelled if they are waiting to run, allowing for any running jobs to finish.

I think if we support auto cancellation for PRs, then we could save many resources.

[supereagle]

@gaocegege Thanks for this good feature request, I think it is necessary to support intelligent policy for auto triggers(both PRs and cron), we will consider this in next version.

[gaocegege]

Thanks, I think we could avoid the situation that some frequent changes in one PR consumes all resources in the Cyclone with the feature.