Clean up workflow template API and CLI
The existing WorkflowTemplate API URLs do not specify a workspace in them, and the workspace is retrofitted in the submitted data for the various create/patch methods. This works until one tries to implement list, which has no workspace information and would require more hacks.
This MR:
- redesigns the API around a standard ViewSet
- removes the previous API endpoints that are not used by debusine client, keeping the rest as legacy for compatibility
- introduces the new API endpoints
- uses the new API endpoints in debusine client
This is a preparatory step for #767 and a more broad extension of the debusine workflow-template subcommand, which can gain list and show like I recently added for collections