spike(v6): add factory methods to Vectorizer namespace

[bevzzz]

Allows vectorizer-first syntax like:

client.collections.create("VectorizedThings",
  c -> c.vectors(
    Vectorizer.none("supplied"),
    Vectorizer.text2vecWeaviate("custom", t2v -> t2v.dimensions(1))));

This PR is more of a POC I put together quickly, as underneath the library still has the "hierarchy" VectorIndex --has-> Vectorizer and not the other way around.

I haven't found a good way to add .vectorIndex to all vectorizer builders without rewriting that hierarchy.

[orca-security-eu]

Orca Security Scan Summary

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[bevzzz]

Here's another thing I had in mind while working on it:

// Using default vector index
Vectorizer.text2VecContextionary(t2v -> t2v.vectorizeCollectionName(false));

// Adding explicit vector index configuration
Vectorizer.<Hnsw.Builder, Hnsw>text2VecContextionary(
    t2v -> t2v.vectorizeCollectionName(false),
    Hnsw::of, hnsw -> hnsw.cleanupIntervalSeconds(30));

// Adding explicit vector index configuration (current syntax)
Hnsw.of(
    Text2VecContextionaryVectorizer.of(t2v -> t2v.vectorizeCollectionName(false)),
    hnsw -> hnsw.cleanupIntervalSeconds(30));