[CLI-10] Overhaul job spec to resemble a DAG

[nravic]

Caltech could use this too, we need to build repeatable, composable and retryable jobs that can be defined as DAGs.

This way, if a step in a DAG fails, the Cedana server retries it on another machine. The composability leads way to some really interesting use cases for users.

We can leverage some of the retryability already written to help build this out.

_{From SyncLinear.com | CLI-10}