[Go] proposal: vector DB Inits return actions

[jba]

Vector DBs only register two actions: an indexer and a retriever.
Continue to allow users to look up these actions by name.
But also return them from Init.

[pavelgj]

LGTM

One use case I'd like to point out, and I think it works fine with this proposal -- initializing multiple vector stores from the plugin:

	cfi, cfr, err := localvec.Init(context.Background(), localvec.Config{
		Name:     "cat-facts",
		Embedder: googleai.Embedder("embedding-001"),
	})
	dfi, dfr, err := localvec.Init(context.Background(), localvec.Config{
		Name:     "dog-facts",
		Embedder: googleai.Embedder("embedding-001"),
	})

Init conveys the semantics well -- you are only allowed to initialize it once per given Name.

[jba]

Actually, I think you've provided a counterexample. I didn't realize you might want to instantiate a vector DB with two indexes in the same program. That makes the vector DB case look more like the generative model case, where there could be multiple named entities of the same kind. Now that I took a better look at your rag test app, I see that you actually use that ability.

So I think for consistency, a single Init should completely initialize the plugin.

Once we have multiple retrievers and indexers, I think pinecone.Retriever("my-index") is the best we can do.

[jba]

...or let's have Init return slices of actions. Best of both worlds.
You can just write actions[0] or actions[1] if there aren't too many, or you can call Name on them.
This also solves the problem of how to know what models were registered when you init a generator plugin with no explicit models, so that it calls ListModels.