Add support for nested query and nested aggregation

[veeraagandhi]

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[Copilot]

Pull Request Overview

This PR adds support for nested query and nested aggregation functionality to the Elasticsearch query parser. The implementation enables handling of nested field aggregations and properly nesting them within the Elasticsearch aggregation structure.

• Enhanced the CombineAggregationsVisitor to detect and handle nested field aggregations automatically
• Modified the SearchDescriptorExtensions to properly copy nested aggregations and their inner structure
• Updated test cases to verify exclusion filters work correctly for nested field aggregations

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 4 comments.

File	Description
CombineAggregationsVisitor.cs	Added logic to detect nested fields and wrap them in nested aggregations with proper structure
SearchDescriptorExtensions.cs	Implemented recursive aggregation copying to handle nested aggregations and their metadata
ElasticNestedQueryParserTests.cs	Updated test to verify multiple nested field aggregations with exclusion filters