Implement NetEvolve.HealthChecks.Azure.CosmosDB package

[Copilot]

This PR adds a comprehensive health check package for Azure Cosmos DB, following the established patterns used by other Azure health check implementations in the repository.

Features

The new NetEvolve.HealthChecks.Azure.CosmosDB package provides:

Multiple Authentication Modes

• Connection String: Direct connection using Cosmos DB connection string
• Account Key: Authentication using service endpoint and account key
• Default Azure Credentials: Uses Azure SDK's default credential chain
• Service Principal: Token-based authentication for service principals

Hierarchical Health Checking

The health check performs verification at multiple levels:

1. Service Availability: Verifies Cosmos DB account is accessible
2. Database Check: Optional verification of specific database (if DatabaseName configured)
3. Container Check: Optional verification of specific container (if ContainerName configured)

Configuration Approaches

Supports both configuration-based and programmatic setup:

// Configuration-based approach
builder.AddCosmosDb("MyCosmosDb");

// Programmatic approach
builder.AddCosmosDb("MyCosmosDb", options =>
{
    options.ConnectionString = "AccountEndpoint=https://...;AccountKey=...";
    options.DatabaseName = "MyDatabase";
    options.ContainerName = "MyContainer";
    options.Timeout = 200;
});

Configuration Structure

{
  "HealthChecks": {
    "CosmosDb": {
      "MyCosmosDb": {
        "ConnectionString": "AccountEndpoint=https://test.documents.azure.com:443/;AccountKey=...",
        "DatabaseName": "TestDatabase",
        "ContainerName": "TestContainer",
        "Mode": "ConnectionString",
        "Timeout": 100
      }
    }
  }
}

Implementation Details

The package includes:

• Client Creation Factory: Thread-safe client caching with support for all authentication modes
• Comprehensive Validation: Mode-specific validation ensuring required properties are configured
• Proper Error Handling: Clear error messages for missing databases/containers
• Performance Optimized: Uses WithTimeoutAsync extension for timeout handling
• Consistent API: Follows same patterns as existing Azure health checks

Testing

Added comprehensive unit tests covering:

• Dependency injection validation
• Options configuration and validation
• Configuration binding scenarios
• Mode-specific validation rules

Integration test structure is provided for future CosmosDB emulator testing.

Fixes #35.

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