v6: Dynamic vector index configuration

[bevzzz]

🧱 Stacked atop #485 (merge that first for a nicer diff)

This PR adds configuration type for Dynamic vector index.

.vectorConfig(
  VectorConfig.selfProvided(v -> v
    .vectorIndex(Dynamic.of(idx -> idx
      .hnsw(Hnsw.of(...))
      .flat(Flat.of(...))
      .threshold(3_000_000)
    )
  )
)

[orca-security-eu]

Orca Security Scan Summary

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