Add support for named vector to enable native support for multi modal use cases

[hsm207]

Is your feature request related to a problem? Please describe.
My document can have different representations e.g. for a movie db, i could have different embeddings for:

1. the movie's title
2. the movie's synopsis
3. the movie's poster

I can't model without creating 3 WeaviateVectorStores.

Describe the solution you'd like
Be able to create 1 WeaviateVectorStore to capture 3 distinct embeddings given a document.

Describe alternatives you've considered
NA

Additional context

• Weaviate's named vector tutorial