Support Aliyun Elasticsearch query encoding

[vicety]

What changed

• Allow the Aliyun Elasticsearch index name and ID field to be overridden with VDBBENCH_ALIYUN_ES_INDEX and VDBBENCH_ALIYUN_ES_ID_FIELD.
• Encode query vectors as big-endian float32 bytes and Base64 before delegating to the Elastic Cloud search implementation.

Why

Aliyun Elasticsearch expects the query vector in its binary Base64 representation, and deployments may use custom index and ID field names.

Validation

The implementation was manually validated by the contributor.

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