EF-281: Support building "Atlas" search indexes

[ajcvickers]

Fluent API for building search indexes.

[Copilot]

Pull request overview

This pull request adds comprehensive support for building MongoDB Atlas search indexes through a fluent API in Entity Framework Core. The feature enables developers to define and create search indexes declaratively through the model builder, with support for both static and dynamic mappings across various field types.

Key Changes

• Introduced fluent API for configuring Atlas search indexes with support for multiple field types (autocomplete, boolean, date, geo, number, objectId, string, token, uuid)
• Added comprehensive test coverage with 4200+ lines of functional tests and negative test cases
• Extended database creation infrastructure to handle search index creation and lifecycle management

Reviewed changes

Copilot reviewed 86 out of 89 changed files in this pull request and generated 11 comments.

Show a summary per file

File	Description
SearchIndexTests.cs	Comprehensive functional tests covering all search index types and configurations
SearchIndexNegativeTests.cs	Error handling tests for invalid search index configurations
MongoDatabaseCreator.cs	Extended to support creating and waiting for search indexes alongside vector indexes
IMongoDatabaseCreator.cs	Interface updates for search index methods
Metadata/Search/*	50+ new classes defining search index structure, builders, and configuration options
SingleEntityDbContext.cs	Refactored to use CollectionNamespace instead of string collection names
ConnectionTests.cs	Updated to use renamed test context class
VectorIndexOptions.cs	Documentation updates changing "Atlas" to "MongoDB"

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