Python: Fix Cosmos DB MongoDB vector index kind mapping (#14104)

[MeiSiristhebest]

Motivation and Context

Fixes #14104.

In python/semantic_kernel/connectors/azure_cosmos_db.py, CosmosMongoCollection._get_index_definitions assigned index_kind from DISTANCE_FUNCTION_MAP_MONGODB[field.distance_function] instead of INDEX_KIND_MAP_MONGODB[field.index_kind].

This caused three issues:

1. cosmosSearchOptions["kind"] was sent as a similarity string (e.g. "COS") rather than a valid vector index kind ("vector-hnsw", "vector-ivf", "vector-diskann"), leading to index creation failure on Azure Cosmos DB for MongoDB vCore.
2. The match index_kind: block never matched any vector-* pattern, so HNSW/IVF tuning parameters (m, efConstruction, numList) were silently dropped.
3. INDEX_KIND_MAP_MONGODB was validated for membership but its mapped value was never used.

Description

Updated CosmosMongoCollection._get_index_definitions to correctly map field.index_kind via INDEX_KIND_MAP_MONGODB[field.index_kind].

Also updated the unit test in test_azure_cosmos_db_mongodb_collection.py to assert that cosmosSearchOptions["kind"] == "vector-hnsw" and cosmosSearchOptions["similarity"] == "COS".

Contribution Checklist

• The code builds clean without any errors or warnings
• The PR follows the SK Contribution Guidelines and the pre-submission formatting script raises no violations
• All unit tests pass, and I have added new tests where possible
• I didn't break anyone 😄

[Copilot]

Pull request overview

This PR fixes a bug in the Python Azure Cosmos DB for MongoDB connector where the vector index kind was incorrectly populated with the distance-function similarity code, causing invalid index definitions and preventing index-kind-specific tuning options from being applied.

Changes:

• Correctly map field.index_kind via INDEX_KIND_MAP_MONGODB when building MongoDB vector index definitions.
• Update the MongoDB collection unit test to assert the expected cosmosSearchOptions["kind"] and ["similarity"] values.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
python/semantic_kernel/connectors/azure_cosmos_db.py	Fixes vector index kind mapping to use the index-kind map (enabling correct vector-* kinds and match-based option handling).
python/tests/unit/connectors/memory/azure_cosmos_db/test_azure_cosmos_db_mongodb_collection.py	Updates assertions to validate kind="vector-hnsw" and similarity="COS".

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[github-actions]

Automated Code Review

Reviewers: 5 | Confidence: 86% | Result: All clear

Reviewed: Correctness, Security Reliability, Test Coverage, Failure Modes, Design Approach

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Automated review by MeiSiristhebest's agents