Configure relationship with foreign key

[jdkandersson]

As a user I want to define multiple relationships on a model pointing to the same referenced model so that I can have a construct such as primary and secondary supervisor of an employee.

Follow on from #139

• [ ] The foreign key fully qualified name needs to be generated for a relationship
• [ ] This needs to be added to the artefacts passed to the relationship facade
• [ ] This needs to be used by the SQLAlchemy relationship constructor with the "foreign_keys" argument
• [ ] A decision needs to be made about whether that parameter is allowed to be in the x-kwargs dictionary and which one to prioritise

[diogohudson]

Hi, community! Is there any ETA for this to be delivered? Or maybe a workaround to get this working?