New API endpoints for announce and scrape requests

[josecelano]

Although you can use the HTTP tracker directly to make announce and scrape requests, I think it would be helpful to do it via the API in some cases. The main advantages would be:

• The response would be a JSON (not bencoded).
• Request parameters like the info_hash and peer_id could use a UTF8 string instead of bytes. That would make it easier for clients to build and send the request.

Some clients could not be BitTorrent clients. They could be other applications like console clients, ...

Some potential use cases:

• Announce torrents from console scripts. For example Need help understanding the announce URL #705 (reply in thread)
• The scrape endpoint could be used by the Index to import torrent statistics in batches. See Import all torrents statistics from the tracker (even with high load and many torrents) torrust-index#469

cc @torrust/torrustaceans

[josecelano]

Relates to: #725