Pulp - Story #3209: As a user, I have Repository Versions
Move sync logic from Importer model to a task
This task is to:
- Create a celery task called `sync` in pulp_file.app.tasks.py
- define a POST detail route called sync on FileImporterViewset that deploys the celery task with reservation for the repository. This viewset should accept `repository` as a POST body parameter.
The logic defined in the task should be taken from models.FileImporter.sync. Validation and setting the working directory from pulpcore.tasks.importer.sync should also be added to this task.