[ZEPPELIN-6196] Improve and Add Unit Tests for Elasticsearch Client and Wrappers

[ParkGyeongTae]

What is this PR for?

This PR improves the test coverage for the Elasticsearch interpreter module by:

• Refactoring and enhancing the existing unit tests in ElasticsearchClientTypeTest and ElasticsearchClientTypeBuilderTest
• Adding new unit tests for AggWrapper and HitWrapper

These changes help ensure better reliability and maintainability of Elasticsearch-related components in Apache Zeppelin.

What type of PR is it?

Improvement

Todos

• [x] - Refactor tests for ElasticsearchClientType and Builder
• [x] - Add new tests for AggWrapper
• [x] - Add new tests for HitWrapper

What is the Jira issue?

• Jira: https://issues.apache.org/jira/browse/ZEPPELIN-6196

How should this be tested?

The following test classes were added or modified:

• ElasticsearchClientTypeTest
• ElasticsearchClientTypeBuilderTest
• AggWrapperTest
• HitWrapperTest

You can verify these tests by running: ./mvnw -pl elasticsearch test

Screenshots (if appropriate)

N/A

Questions:

• Does the license files need to update? No.
• Is there breaking changes for older versions? No.
• Does this needs documentation? No.