Add path-level metrics feature with configurable status filtering

[mosheharary-ts]

This commit implements a new optional feature for tracking HTTP requests at the path level, grouped by zone, path, and HTTP status code. Key changes:

Core functionality:

• Add new metric cloudflare_zone_requests_status_path with labels for zone, account, status, and path
• Implement path normalization to strip query strings and fragments for reduced cardinality
• Add configurable path limit per zone (1-1000, default 100) to control metric cardinality
• Add status code filtering with support for individual codes, ranges, or combinations
• Disable path metrics for free-tier accounts as this requires premium Cloudflare features
• Fetch path metrics using new GraphQL query with adaptive grouping

Configuration:

• Add ENABLE_PATH_METRICS flag (default: false) to enable the feature
• Add PATH_METRICS_LIMIT flag (default: 100) to control max paths per zone
• Add PATH_METRICS_STATUS_FILTER flag to filter by HTTP status codes

Documentation:

• Update README.md with usage examples for path metrics and status filtering
• Add Helm chart configuration for pathMetrics.enabled and pathMetrics.limit
• Update chart README with usage examples and cardinality warnings

Docker and testing:

• Add Dockerfile with multi-stage build using Go 1.25 and Alpine
• Add docker-compose.yml with Prometheus integration for local testing
• Add prometheus.yml configuration for scraping the exporter
• Add env.example template for API token configuration
• Add comprehensive tests for path metrics validation and label structure

This feature addresses PLTOPS-4619 and provides enhanced visibility into request patterns at the path level for detailed traffic analysis.

Pull Request Template

Description

Please provide a brief description of the changes in this PR.

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update
• Code refactoring
• Other (please describe):

Testing

• I have run make release-tests and all tests pass
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes

Code Quality

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation

Before Submitting

Please ensure you have completed the following before submitting your PR:

# Run comprehensive tests
make release-tests

If the above command fails, please fix the issues before submitting your PR.

Additional Notes

Add any other context about the pull request here.

[haad]

Can anyone test this PR on account with multiple zones ? @aw or @sprsquish ?