HTTP Tracker Client: add `scrape` request

[josecelano]

Currently you can use the HTTP Tracker client to make an announce request:

$ cargo run --bin http_tracker_client https://tracker.torrust-demo.com 9c38422213e30bff212b30c360d26f9a02136422 | jq
    Finished dev [optimized + debuginfo] target(s) in 0.09s
     Running `target/debug/http_tracker_client 'https://tracker.torrust-demo.com' 9c38422213e30bff212b30c360d26f9a02136422`
{
  "complete": 1,
  "incomplete": 0,
  "interval": 300,
  "min interval": 300,
  "peers": []
}

I'm going to add the scrape so we can also use it in the Tracker Checker.

cargo run --bin http_tracker_client announce https://tracker.torrust-demo.com 9c38422213e30bff212b30c360d26f9a02136422 
cargo run --bin http_tracker_client scrape https://tracker.torrust-demo.com 9c38422213e30bff212b30c360d26f9a02136422

[josecelano]

The output:

$ cargo run --bin http_tracker_client scrape https://tracker.torrust-demo.com 9c38422213e30bff212b30c360d26f9a02136422 | jq
    Finished dev [optimized + debuginfo] target(s) in 0.07s
     Running `target/debug/http_tracker_client scrape 'https://tracker.torrust-demo.com' 9c38422213e30bff212b30c360d26f9a02136422`

{
  "9c38422213e30bff212b30c360d26f9a02136422": {
    "complete": 0,
    "downloaded": 0,
    "incomplete": 0
  }
}