vectorstore/options: Extending Vectorstore options to accept optional embedder

[nidzola]

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Description

• this option allows us to use different embedders, if we have single vectorstore (like posgresql) which can handle (storing/using) multiple embeddings.

Usage example:

....
        // dummy list of embedders
        embedders := map[string]embedder.Embedder{
		"openai": openaiEmbedder,
		"huggingface": huggingfaceEmbedder,
		"vertexai": vertexaiEmbedder,
		"someother": someotherEmbedder,
	}
        emd := embedders["openai"] // dummy example pulling the embedders from the list of supported embedders

 	result, err := chains.Run(
		context.TODO(),
		chains.NewRetrievalQAFromLLM(
			llm,
			vectorstores.ToRetriever(store, 5, vectorstores.WithNameSpace(id), vectorstore.WithEmbedder(emb)),
		),
		"What colors is each piece of furniture next to the desk?",
	)
....

from this point on, our store when the AddDocuments or SimilaritySearch methods are called from the vectorstore interface, we can actually use the needed embedder and not be tied to only one.

for example

// Store is a wrapper around the pinecone rest API and grpc client.
type Store struct {
	some store configuration where we could have or not have embedder
}

funct (s Store) AddDocuments(ctx context.Context, docs []schema.Document, options ...vectorstores.Option) error {
     opts := v.getOptions(options...)
     vectors, err := options.Embeder.EmbedDocuments(ctx, texts)
   ....
}

[nidzola]

@tmc