Add OpenAPI Docs

[u8sand]

Using the Playbook REST API

• Probably needs a standardized API documentation of inputs/outputs - sherry xie

• Could add more textual explanations - sherry xie

• How workflow arguments are constructed more generally for each type of node - sherry xie

• Document all possible node constructions somewhere (maybe overkill) → otherwise users kind of have to search through code to find the node names - sherry xie

• Could clarify that the returned IDs can be used to view both the UI and in JSON format - sherry xie

If possible, a swagger page would be very useful for users to know what is possible and how to format calls. If not, more extensive documentation would be great. - Sean Kim