Workflows service and updated core API schemas

[berggren]

Summary

Adding WorkflowsService for management of workflows and their associated tasks.

Key Changes

• WorkflowsService: Implemented Create, Run, Status, and Get methods.
  • Methods use ID-based parameters (folderID, workflowID) for flexibility.
  • Create includes automatic folder ID resolution from input files with validation.
• Model Updates:
  • Added Folder field to the File struct.
  • Added UUID and Description fields to the Folder struct.
  • Introduced Workflow, Task, and WorkflowStatus structures.
• Client Enhancements:
  • Updated the Error struct to include and display an underlying Cause.
  • Initialized WorkflowsService in the main Client.
• Testing: Added workflows_test.go with 100% coverage of new service methods, including error paths and folder resolution logic.