When creating or updating workflows, we should do additional validation of steps, states and workflows #24
Description
Currently, you can make calls to create workflows or update steps and there is no validation to ensure you have:
(1) selected a valid workflow
(2) selected a valid step that belongs in your chosen workflow
(3) selected the correct repository for the workflow
It does verify that the state is valid, however.
It would be useful to have some validation either at the gem level or at the service level (i.e. in https://github.com/sul-dlss/workflow-service) to prevent bad workflow entries from being inadvertently created by consumers (which can lead to odd inconsistencies in reports and in argo)