Add `metadata` support to `addDocuments`

[andrewgleave]

Great library.

Unlike the TS and Python client libraries, it isn't possible to attach an array metadata dictionaries using the Chroma.addDocuments API.

It would be very useful to have parity so I don't need to maintain and sync a CoreData with Chroma just for meta.

Simply metadata: [String: String] would meet most needs.

[ozziek]

+1 would also be great to be able to access the embeddings, e.g. in python:

collection = client.get_collection("<name>")
documents = collection.get(include=["documents", "embeddings"])
print(documents)