feat(index): add vector index option surface and validation

[chrevanthreddy]

Describe the issue this Pull Request addresses

Resolves #19096 (umbrella: #19094, RFC-109)

First foundational slice of RFC-109 (Hudi Native Vector Index): the option surface and validation for vector indexes. This PR is intentionally scoped to the self-contained option/config layer so it compiles and tests standalone; the DDL command dispatch, MDT schema/payload, and bootstrap execution land in dependent follow-up PRs (#19097, #19099, …) where their partition-type and executor dependencies are introduced.

Summary and Changelog

• Add org.apache.hudi.common.index.vector.VectorIndexOptions — the full OPTIONS(...) key surface for CREATE INDEX ... USING VECTOR (dimension, metric, algorithm, quantizer, cluster/probe/refine counts, RaBitQ bits/seed/storage/posting layout, search-time flags) with typed accessors, defaults, and early validation.
• Add VectorIndexType — routing algorithm enum (IVFFLAT, IVFPQ_HNSW) with case/separator-insensitive parsing.
• Add VectorDistanceMetric — COSINE / L2 / DOT_PRODUCT distance enum (min-heap-consistent distances) with parsing.
• Add PARTITION_NAME_VECTOR_INDEX / PARTITION_NAME_VECTOR_INDEX_PREFIX constants to HoodieTableMetadataUtil.
• Add TestVectorIndexOptions — 9 unit tests covering defaults, metric/algorithm parsing, and early-failure on invalid configs (missing dimension, invalid metric, out-of-range RaBitQ bits).

Impact

No behavioral impact on existing tables or code paths. Adds new, unreferenced option/enum classes plus two constants. No schema, writer, reader, or DDL execution changes in this PR.

Risk Level

none

New self-contained classes + two constants + unit tests; nothing wires into existing runtime paths yet.

Documentation Update

Option semantics are documented as Javadoc on each option key. The user-facing RFC document is tracked separately (see #19309). No site docs change required until the feature is user-invokable.

Contributor's checklist

• Read through contributor's guide
• Change Logs and Impact described above
• Necessary doc changes done or have another open PR
• For large changes, please consider breaking it into sub-tasks under an umbrella issue (RFC-109: MDT-backed vector index umbrella tracking issue #19094)

[hudi-bot]

CI report:

• de7e166 UNKNOWN

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