Add: manifest.json

[dnzbk]

Description

• migration from a file header config definition to a manifest.json-based configuration;
• works with NZBGet v23.1 and above;
• no longer works with NZBGet v22 and below;
• added more tests;

Testing

By @dnzbk with NZBGet v23.1 on:

• Windows 11;
• Debian 12;