Add NetEvolve.HealthChecks.AWS.EC2 health check package

[Copilot]

This PR adds a new health check package for AWS Elastic Compute Cloud (EC2) service, following the established patterns used by other AWS health check packages (S3, SQS, SNS).

What's Added

Core Implementation

• ElasticComputeCloudHealthCheck: Uses DescribeRegionsAsync API to verify EC2 service connectivity
• ElasticComputeCloudOptions: Configuration class supporting AWS credentials, region endpoint, service URL, and timeout settings
• ElasticComputeCloudConfigure: Handles configuration binding from HealthChecks:AWSEC2 section with validation
• DependencyInjectionExtensions: Provides AddAWSEC2() extension method with proper service registration
• CreationMode: Enum for authentication modes (BasicAuthentication support)

Usage Examples

Configuration-based approach:

var builder = services.AddHealthChecks();
builder.AddAWSEC2("MyEC2Check");

{
  "HealthChecks": {
    "AWSEC2": {
      "MyEC2Check": {
        "Region": "us-west-2",
        "AccessKey": "...",
        "SecretKey": "...",
        "Timeout": 1000
      }
    }
  }
}

Builder-based approach:

builder.AddAWSEC2("MyEC2Check", options => {
    options.RegionEndpoint = RegionEndpoint.USWest2;
    options.AccessKey = "...";
    options.SecretKey = "...";
    options.Timeout = 1000;
});

Testing & Documentation

• Unit tests: Complete test coverage following TUnit patterns with argument validation
• Integration tests: LocalStack-based tests for both configuration and options approaches
• Documentation: Comprehensive README with usage examples and configuration options
• Bundle integration: Updated AWS bundle package to include EC2 health check

Project Structure

The implementation follows the exact same structure and naming conventions as existing AWS services:

• Project references added to both unit and integration test projects
• AWSSDK.EC2 package dependency included in integration tests
• Consistent file organization and API design

The health check uses a lightweight DescribeRegionsAsync call with MaxResults = 1 to verify EC2 service connectivity while minimizing API overhead.

Fixes #52.

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