[python-nextgen] Add datetime, date format support (#14799)

* add datetime, date format support in python nextgen

* encode query parameters

* update default datetime format

* change default datetime format

samples/client/echo_api/python-nextgen/openapi_client/configuration.py

@@ -175,6 +175,14 @@ class Configuration(object):
         """Options to pass down to the underlying urllib3 socket
         """
 
+        self.datetime_format = "%Y-%m-%dT%H:%M:%S.%f%z"
+        """datetime format
+        """
+
+        self.date_format = "%Y-%m-%d"
+        """date format
+        """
+
     def __deepcopy__(self, memo):
         cls = self.__class__
         result = cls.__new__(cls)