Registry tool: "--dry-run" flags could produce messy results when used with concurrency

[timburks]

Several compute subcommands accept --dry-run flags that cause them to print generated values instead of saving them in artifacts. But because these prints occur in tasks, I think (but haven't observed) that they could occur simultaneously, leading to garbled output. I've never used these flags, so I'm not strongly favoring keeping them, but if we do, should we force --jobs to 1? Or should we only allow --dry-run with patterns that match single resources?

Also, what exactly should we be outputting (raw artifacts or Registry YAML)?