Problem Description: 

Both PAH and CAH will perform a collection signature during promotion process.

API will also provide an endpoint to allow the sign of a specific collection version.

QA Criteria: 

• Using the django_shell it is possible to sign a specific collection version by providing its ID + the name of the signing service
• The result of the task is a new ContentSignature created and served on signatures API (TBD)

Proposed Solution: 

On galaxy_ng/app/tasks a general task will take an artifact pointer (e.g: collection_version_id) and the name of a registered signing-service and perform the sign workflow.

Reminder: Backend task