Implement TLS keylog functionality for HTTP Toolkit

- Add SSL keylog configuration to generateHTTPSConfig function
- Create keylog directory structure in config path
- Configure incoming and upstream keylog file paths
- Update package.json to use local mockttp dependency
- Fix mockttp build issues and TypeScript type annotations
- Add GraphQL subscription support for tls-keylog events
- Verify keylog functionality generates NSS Key Log format data
- Enable TLS traffic decryption with Wireshark and Chrome DevTools

Author: HTTP Toolkit Developer