Allow to specify loads for the embeddings

[olivermt]

It does not seem the current dsl and/or embedding_model thing has a structured way to define loads.
In ecommerce you typically want to pull from at least 3-4 resources to make a relevant vector for a given product for example.

Also would be cool if you could define the prompt with an expr

[zachdaniel]

Good idea :) PRs welcome! 🙇 I might get to it soon but I gotta take a bit of time to work on other things.

[olivermt]

I am at least two or three months out from our big eComm re-write-launch on ash, if someone hasn't done this by then I'll pick it up :) Just figured I'd make a note before I forgot.