Relates to: #614

For testing purposes, it would be very helpful to have a command like this:

cargo run --bin udp_tracker_client https://tracker.torrust-demo.com 9c38422213e30bff212b30c360d26f9a02136422

This script can be used to manually test the HTTP tracker but also for E2E tests in the future.