New factory DSL options:
1. `auto_build` allows you to provide a list of relationships which must also be built when building that factory.
2. `auto_load` allows you to provide a load statement for relationships and calculations that must be loaded when building that factory.
Reviewed-on: #83
Co-authored-by: James Harton <james@harton.nz>
Co-committed-by: James Harton <james@harton.nz>
