Duplicate a project (or save it as a template)

Copies the project's structure: sections, tasks, subtasks, priorities, categories and tags. Progress, assignees, dates, comments and attachments are reset, and members are not carried over; the caller becomes the copy's owner. With as_template: true the copy gets status template, which is what the new-project template picker lists; create a project FROM a template by duplicating the template without that flag. Any project member; guests cannot duplicate.