Allow user to know fact's origin
Facts can come from various sources, including the Discovery image, Puppet, Ansible, Salt, Chef...
The user has no way of determining which fact comes from where. The fact importers could easily set an 'origin' field to FactValue that each of the 'FactImporter' subclasses override. e.g: PuppetFactValue#origin is :puppet.
The origin field has to be set on FactValue, and not on FactName, as two sources of facts may provide the facts for the same FactName.
Based on these facts, the user can see in the facts table which facts come from where, which can be useful.
This field should be shown in API responses as well.