[ZEPPELIN-6192] Enhance getHit() safety in ActionResponse and improve interface documentation

[ParkGyeongTae]

What is this PR for?

This PR improves the robustness and clarity of the Elasticsearch interpreter module in Zeppelin.

• Reimplemented ActionResponse#getHit() to throw NoSuchElementException instead of relying on unchecked access to the first hit.
• Introduced a new method getFirstHit() which returns an Optional<HitWrapper> for safer optional access.
• Added and refined Javadoc comments in:
  • ActionResponse.java for both getHit() and getFirstHit()
  • ElasticsearchClient.java to improve clarity on interface usage

What type of PR is it?

Documentation Refactoring

Todos

• [x] Refactor getHit() to throw a safe exception
• [x] Add getFirstHit() method using Optional

What is the Jira issue?

• https://issues.apache.org/jira/browse/ZEPPELIN/ZEPPELIN-6192

How should this be tested?

• Build Test
• Elasticsearch Interpreter Test

Screenshots (if appropriate)

Questions:

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