Add PipraPay payment gateway plugin

Introduces the PipraPay payment gateway integration for XBoard, including plugin registration, configuration, payment processing, webhook handling, and amount verification. Updates the Plugin model to support PipraPay and provides documentation and configuration files for setup.

Author: FakeErrorX

app/Models/Plugin.php

@@ -39,6 +39,7 @@ class Plugin extends Model
         'smogate',        // Smogate
         'telegram',       // Telegram
         'uddoktapay',     // UddoktaPay
+        'piprapay',       // PipraPay
     ];
 
     protected $guarded = [