The range deletion task document create+persist logic is currently scattered in the migration coordinator and migration destination manager. Purpose of this ticket is to enclose in a common function that logic, in order to avoid code duplication.

This is also a precondition for the introduction of a command that will persist range deletion task documents for unowned non-empty ranges, since we want to avoid duplicating the code again with the risk of forgetting to update it once a some field is added/remove.