add "no act" and "limit" cmd line options to see what would be deleted

This script was super helpful when my kubernetes based gitlab runner had an issue and re-registered itself over 300 times.

I added a "-n" option for "no action". It prints out what would be deleted and takes no action.

I also added a "--limit" option to limit the number of runners that are deleted. That can help reduce blast radius when deleting runners.

Anyway - wanted to suggest these changes in case you want to pull them in too.

Thanks!