ATLAS-5194: Add pagination while fetching relationships of an entity

[sheetalshah1007]

What changes were proposed in this pull request?

Added a new disableDefaultSorting boolean parameter to the searchRelatedEntities API across the REST layer, service interface, and implementation. When false (default), the API maintains backward compatibility by applying default "name" sorting if no explicit sortBy is provided. When true, no default sorting is applied, returning results in natural graph traversal order.

Fixed a critical bug in approximate count calculation where deleted entities were incorrectly included in the count when excludeDeletedEntities=true - the implementation now correctly filters by end vertex status instead of edge status.

Updated all existing tests to use disableDefaultSorting=false to preserve current behaviour, and added new test cases to verify sorting logic and accurate count calculation.

Why It Was Needed?

The existing searchRelatedEntities API always applied default "name" sorting even when users didn't specify a sortBy parameter, which could impact performance for large datasets where users don't need sorted results. This forced sorting behaviour couldn't be disabled, making deep pagination slower than necessary. The new parameter gives users the flexibility to opt out of default sorting when they prioritise performance over order, particularly useful for paginated queries on entities with thousands of relationships.

How was this patch tested?

• Unit tests: Updated existing test cases in DiscoveryRESTTest, EntityDiscoveryServiceTest, and AtlasDiscoveryServiceTest to pass disableDefaultSorting=false, ensuring backward compatibility
• New test cases: Added testSearchRelatedEntitiesWithDisableDefaultSorting() to verify both sorted (disableDefaultSorting=false) and unsorted (disableDefaultSorting=true) paths return the same entities
• Pagination tests: Added testSearchRelatedEntitiesWithOffset() to verify correct pagination behaviour across multiple pages
• Edge case tests: Added tests for deleted entity filtering (testSearchRelatedEntitiesWithDeletedEntities) and approximate count accuracy (testApproximateCountExcludesDeleted) with the new parameter
• Manual testing: Tested with curl commands on large datasets (50K-100K relationships) to verify performance improvements and correctness
• No regression for sorted queries

[pinal-shah]

Please review if there is need to introduce new API

[pinal-shah]

Please incorporate changes in the existing method, to avoid code duplication