`get_or_create_collection` should take an (optional) embedding function

[levand]

Both get_collection and create_collection take an embedding function, get_or_create_collection should too for parity.

[HammadB]

So it looks like the local.py and fastapi.py implementations do in fact take the embedding function and plumb it through. But just the abstract class does not highlight it. #307 addresses this.

I wish there was a way for the typechecker to check override issues like this...

[HammadB]

Closed by #307