Allow override for preload in Dataloader Ecto

[jfrolich]

We can already override run_batch, but preload is hard coded. It would be nice to be able to add a customizable preload here.

[benwilson512]

Hi @jfrolich can you elaborate?

[jfrolich]

🙈Can't remember anymore. Sorry for this poorly described issue. I can remember I had some dirty workaround so I will probably run into this later on, and then try to create a better issue.

[benwilson512]

All good!