Add class helper ChatAction (#803)

* Add class helper ChatAction

* Change using helper to using enum.Enum

* Add test for class ChatAction

* Use black formatting

* Add pull request description to CHANGES

* Add test coverage

* Use AutoName class for enum values

* Move `AutoName` to separate file

* Move inheritance from `str`

* Fix failing mypy

* Delete old actions

Co-authored-by: Evgen Fil <evgfilim1@yandex.ru>

aiogram/utils/enum.py

@@ -0,0 +1,8 @@
+import enum
+from typing import Any, List
+
+
+class AutoName(str, enum.Enum):
+    @staticmethod
+    def _generate_next_value_(name: str, start: int, count: int, last_values: List[Any]) -> str:
+        return name.lower()