[DX] Add fixtures and example factories

[NoResponseMate]

Dev setup is a bit lacking;
Right now after running fixtures, you need to also remember about first running the setup command and then the synchronization command. It would be nice to have a method of setting both of these actions to be triggered automatically via fixtures.

I'd see it as split between two nodes:

1. the base association type
2. triggering synchronization in sync (alternatively instead of a fixture this could be a listener after all have been run, but with a fixture, there'd be more flexibility)