New deploy: breaks when step id changes

[josephjclark]

If you change a step id in workflow.yaml, you'll get errors on deploy.

This comes from problems in from-fs, I think because it fails to reconcile the new step in the local workflow against the stuff in the project.yaml file.

I think like #1171 , this comes back to doing a merge when loading from the file system. That should reconcile all changes - and if it doesn't, that just means a new fix in merge and load