feat: Add CloudFormation resource counting feature

[hoegertn]

Description

This PR adds a new resource counting feature that monitors CloudFormation resource usage across stacks during the CDK synthesis step. The feature helps teams stay aware of CloudFormation's 500 resource per stack limit and provides warnings when approaching this threshold.

Changes

New Features

• Resource Counter Tool (src/awscdk/count-resources.ts): A new CLI tool that analyzes CloudFormation templates in the cloud assembly and counts resources per stack
• ResourceCountStep (src/awscdk/resource-count-step.ts): A new pipeline step that integrates resource counting into CI/CD workflows
• Configuration Options: Added two new options to CDKPipelineOptions:
  • enableResourceCounting (default: true): Toggle resource counting on/off
  • resourceCountWarningThreshold (default: 450): Configurable warning threshold

Pipeline Integration

• GitHub: Automatically creates a PR workflow that counts resources and comments on pull requests with detailed resource usage tables
• GitLab: Automatically creates an MR job that posts resource count summaries to merge requests
• Bash: Supports resource counting in bash-based pipelines

Output Formats

• Console output with per-stack breakdown and warnings
• JSON results file (resource-count-results.json) for programmatic access
• GitHub step summary integration for workflow visibility
• PR/MR comments with formatted tables and recommendations

Benefits

• Early detection of stacks approaching CloudFormation limits
• Actionable recommendations for stack optimization
• Visibility into resource usage across the entire infrastructure
• Helps prevent deployment failures due to resource limit violations

Configuration

Users can control the feature via pipeline options:

new GithubCDKPipeline(this, {
  enableResourceCounting: true,
  resourceCountWarningThreshold: 450,
  // ... other options
});

The feature is enabled by default but can be disabled by setting enableResourceCounting: false.