Changes to Create a workflow definition.

added the non-success response with the status 403

added the non-success response with the status 415

added the non-success response with the status 422

the response property details became nullable for the status 400

the response property details became nullable for the status 404

the response property details became nullable for the status 409

the response property details became nullable for the status 500

added the new optional request property arbitrary_json

added the optional property arbitrary_json to the response with the 201 status

added the new optional request property nodes/items/preferred_skills

added the optional property nodes/items/preferred_skills to the response with the 201 status

endpoint added