New E2E test: download torrent in private mode

[josecelano]

It only checks that downloading a torrent works in private mode. This PR does not check that the downloaded torrent contains the tracker keys. The index should have a test for that.

Sample torrent with tracker keys (in JSON):

{
   "announce": "http://tracker:7070//3PISvzYph3GYkjJvz39hhnUqANLeVC7r",
   "announce-list": [
      [
         "http://tracker:7070//3PISvzYph3GYkjJvz39hhnUqANLeVC7r"
      ],
      [
         "udp://tracker.torrust-demo.com:6969"
      ],
      [
         "udp://tracker.coppersurfer.tk:6969/announce"
      ],
      [
         "udp://9.rarbg.com:2710/announce"
      ],
      [
         "udp://p4p.arenabg.com:1337"
      ],
      [
         "udp://tracker.leechers-paradise.org:6969"
      ],
      [
         "udp://tracker.internetwarriors.net:1337"
      ],
      [
         "udp://tracker.opentrackr.org:1337/announce"
      ],
      [
         "http://tracker.openbittorrent.com:80/announce"
      ],
      [
         "udp://opentracker.i2p.rocks:6969/announce"
      ],
      [
         "udp://tracker.internetwarriors.net:1337/announce"
      ],
      [
         "udp://tracker.leechers-paradise.org:6969/announce"
      ],
      [
         "udp://coppersurfer.tk:6969/announce"
      ],
      [
         "udp://tracker.zer0day.to:1337/announce"
      ]
   ],
   "creation date": 1713791389,
   "info": {
      "files": [
         {
            "length": 2142878501,
            "path": [
               "Spirited.Away.2001.1080p.BluRay.x264-[YTS.AM].mp4"
            ]
         },
         {
            "length": 58132,
            "path": [
               "www.YTS.AM.jpg"
            ]
         }
      ],
      "name": "Spirited Away (2001) [BluRay] [1080p] [YTS.AM]",
      "piece length": 524288,
      "pieces": "<hex>1D 99 72 BF 0A E7 F0 D8 61 86 D7 AE 3B 59 A9 EF FA 5E CB 04 2D DB 14 04 A3 C0 82 0E DA 0B 7F 73 E5 5B 07 84 31 45 0C 06 4C BF 59 22 89 87 82 6B 71 D9 A8 A4 3C ... 20 4C 80 FB C7 EA</hex>"
   }
}

[josecelano]

ACK 7e670083d5468281c2a38a8eb2b43a690880b9e8