Add V2 Facets and Searchabilities API Support

[aandrukhovich]

Add V2 Facets and Searchabilities API Support

Summary

This PR adds support for the V2 versions of the /v2/facets and /v2/searchabilities endpoints, running in parallel with the existing V1 implementations.

Changes

New Facets V2 Methods

• CreateFacetConfigV2 - Create a single facet configuration
• GetAllFacetConfigsV2 - Retrieve all facet configurations with pagination
• GetFacetConfigV2 - Get a specific facet by name
• CreateOrReplaceFacetConfigsV2 - Batch create or replace facets (PUT)
• BatchPartiallyUpdateFacetConfigsV2 - Batch partial update facets (PATCH)
• ReplaceFacetConfigV2 - Replace a single facet configuration
• PartiallyUpdateFacetConfigV2 - Partially update a single facet
• DeleteFacetConfigV2 - Delete a facet configuration

New Searchabilities V2 Methods

• RetrieveSearchabilitiesV2 - Retrieve searchabilities with filtering/pagination
• GetSearchabilityV2 - Get a specific searchability by name
• PatchSearchabilitiesV2 - Batch create or update searchabilities
• PatchSearchabilityV2 - Update a single searchability
• DeleteSearchabilitiesV2 - Batch delete searchabilities
• DeleteSearchabilityV2 - Delete a single searchability

New Models

• FacetV2 - V2 facet model with new fields (Countable, OptionsLimit, Hierarchical type, CreatedAt, UpdatedAt)
• FacetTypeV2 - Enum adding Hierarchical type
• FacetV2GetAllResponse - Response wrapper for listing facets
• SearchabilityV2 - V2 searchability model with new fields (Displayable, Hidden, CreatedAt, UpdatedAt)
• SearchabilitiesV2Response - Response wrapper for searchabilities operations
• RetrieveSearchabilitiesV2Request - Request object with filtering/sorting options
• PatchSearchabilitiesV2Request - Request object for batch create/update
• DeleteSearchabilitiesV2Request - Request object for batch delete

V2 API Differences from V1

Facets:

• New Hierarchical facet type
• New Countable field (skip counting for high-cardinality facets)
• New OptionsLimit field (limit options returned in search)
• New CreatedAt/UpdatedAt timestamps
• Uses path_in_metadata instead of inferring from name

Searchabilities:

• Removes percentage_presence, example_items, and type fields
• Adds Displayable and Hidden fields
• Adds CreatedAt/UpdatedAt timestamps
• Simplified query parameter filtering (direct boolean params vs nested filters)

Test Plan

• Added FacetTestsV2.cs with 15 test cases covering all facet operations
• Added SearchabilityTestsV2.cs with 12 test cases covering all searchability operations
• All tests include proper cleanup in OneTimeTearDown
• Solution builds successfully

Breaking Changes

None. V2 methods are additive and V1 methods remain unchanged.