Use django helper to import variants

Author: Hugo Osvaldo Barrera

payments/core.py

@@ -1,5 +1,4 @@
 import re
-from importlib import import_module
 from typing import TYPE_CHECKING
 from typing import Dict
 from typing import Optional
@@ -155,9 +154,7 @@ def _default_provider_factory(variant: str, payment: Optional["BasePayment"] = N
     if not handler:
         raise ValueError("Payment variant does not exist: {}".format(variant))
     if variant not in PROVIDER_CACHE:
-        module_path, class_name = handler.rsplit(".", 1)
-        module = import_module(module_path)
-        class_ = getattr(module, class_name)
+        class_ = import_string(handler)
         PROVIDER_CACHE[variant] = class_(**config)
     return PROVIDER_CACHE[variant]