Describe the feature you'd like to request

Add support for --plan flag that will output JSON that includes information about what is about to happen for a given command. This can be used with scripts such as Vercel's Ignore Build Command and also in Circle and GitLab for dynamic provisioning of CI/CD workflows.

Describe the solution you'd like

Collect up info through a traversal and print out to JSON

• Should this hit caches / wonder if we need an endpoint specifically to check without downloading which we don't yet support?

Describe alternatives you've considered

• Possibly need to do another full pass through the graph / topological sort in order to hash
• Split up scheduler so that the graph generation and execution occur in separate steps (so that it can be interrupted if --plan is passed)