Add proxy support to Load Tester

- Introduced a new ProxyURL field in the Config struct to allow users to specify a proxy for requests.
- Updated command-line flags to include a proxy option.
- Enhanced the load testing functionality to configure the HTTP client to use the specified proxy.
- Updated README with examples for using the proxy feature, including support for HTTP, SOCKS5, and authenticated proxies.

Refactor Brutal Load Tester to use Cobra CLI framework

- Replaced TUI with a modern CLI interface powered by Cobra.
- Simplified command structure, allowing URL input as an argument or flag.
- Enhanced configuration options with flags for method, headers, body, and output.
- Added shell completion support for Bash, Zsh, Fish, and PowerShell.
- Updated README to reflect new features and usage examples.
- Removed unused dependencies and cleaned up code for better maintainability.

Update release workflow to trigger on all tags instead of just 'v*'