Make Slosher Job-Generating UI

Let's make the generating of slosher "job" files (yaml) fun and easy with a high-level UI.

## Requirements
* create a job.
* add steps to it.
* save the result to a yaml file.
* validate that it is a valid job with the `Job` pydantic model.
* nice-to-have: "create-from-previous-job."
* make a copy of an existing job file (i.e: remove the historical metadata, but keep everything else)