[PYTHON] use customized default Configuration() objects if configured by the programmer (#8500)

Author: adpoliak

.generator/templates/api_client.mustache

@@ -61,7 +61,7 @@ class ApiClient(object):
     def __init__(self, configuration=None, header_name=None, header_value=None,
                  cookie=None, pool_threads=1):
         if configuration is None:
-            configuration = Configuration()
+            configuration = Configuration.get_default_copy()
         self.configuration = configuration
         self.pool_threads = pool_threads