Adjust getIndexInfo to return an empty ResultSet instead of a null value

[Paultagoras]

Summary

• Tweaked DatabaseMetaData.getIndexInfo to return an empty ResultSet rather than null

Closes #2286

Checklist

Delete items not relevant to your PR:

• Closes #
• Unit and integration tests covering the common scenarios were added
• A human-readable description of the changes was provided to include in CHANGELOG
• For significant changes, documentation in https://github.com/ClickHouse/clickhouse-docs was updated with further explanations or tutorials

[Copilot]

Pull Request Overview

This PR updates DatabaseMetaData.getIndexInfo to return an empty ResultSet instead of null, ensuring that JDBC calls do not unexpectedly receive a null value. It also renames the DatabaseMetaData class to DatabaseMetaDataImpl and updates its references, and adds a new integration test for the getIndexInfo behavior.

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
jdbc-v2/src/test/java/com/clickhouse/jdbc/metadata/DatabaseMetaDataTest.java	Updated test to reference DatabaseMetaDataImpl and assert an empty ResultSet for getIndexInfo
jdbc-v2/src/main/java/com/clickhouse/jdbc/metadata/DatabaseMetaDataImpl.java	Renamed class from DatabaseMetaData and modified getIndexInfo to return an empty ResultSet using a SQL query
jdbc-v2/src/main/java/com/clickhouse/jdbc/ConnectionImpl.java	Updated to import and reference DatabaseMetaDataImpl instead of the previous class

[sonarqubecloud]

Quality Gate failed

Failed conditions
7 Security Hotspots
29.6% Coverage on New Code (required ≥ 80%)
34.8% Duplication on New Code (required ≤ 3%)
E Reliability Rating on New Code (required ≥ A)

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[chernser]

I would expect that we use https://clickhouse.com/docs/sql-reference/statements/show#show-index to get information about indexes.

[mzitnik]

LGTM