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]

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