Bot API 5.7 and some new features (#834)

* Update API, added some new features

* Fixed unknown chat_action value

* Separate events from dispatcher messages

* Disabled cache for I18n LazyProxy

* Rework events isolation

* Added chat member status changed filter, update Bot API 5.7, other small changes

* Improve exceptions in chat member status filter

* Fixed tests, covered flags and events isolation modules

* Try to fix flake8 unused type ignore

* Fixed linter error

* Cover chat member updated filter

* Cover chat action sender

* Added docs for chat action util

* Try to fix tests for python <= 3.9

* Fixed headers

* Added docs for flags functionality

* Added docs for chat_member_updated filter

* Added change notes

* Update dependencies and fix mypy checks

* Bump version

docs/dispatcher/flags.rst

@@ -0,0 +1,89 @@
+=====
+Flags
+=====
+
+Flags is a markers for handlers that can be used in `middlewares <#use-in-middlewares>`_
+or special `utilities <#use-in-utilities>`_ to make classification of the handlers.
+
+Flags can be added to the handler via `decorators <#via-decorators>`_,
+`handlers registration <#via-handler-registration-method>`_ or
+`filters <via-filters>`_.
+
+Via decorators
+==============
+
+For example mark handler with `chat_action` flag
+
+.. code-block:: python
+
+    from aiogram import flags
+
+    @flags.chat_action
+    async def my_handler(message: Message)
+
+Or just for rate-limit or something else
+
+.. code-block:: python
+
+    from aiogram import flags
+
+    @flags.rate_limit(rate=2, key="something")
+    async def my_handler(message: Message)
+
+Via handler registration method
+===============================
+
+.. code-block:: python
+
+    @router.message(..., flags={'chat_action': 'typing', 'rate_limit': {'rate': 5}})
+
+Via filters
+===========
+
+.. code-block:: python
+
+    class Command(BaseFilter):
+        ...
+
+        def update_handler_flags(self, flags: Dict[str, Any]) -> None:
+            commands = flags.setdefault("commands", [])
+            commands.append(self)
+
+
+
+Use in middlewares
+==================
+
+.. automodule:: aiogram.dispatcher.flags.getter
+    :members:
+
+Example in middlewares
+----------------------
+
+.. code-block:: python
+
+    async def my_middleware(handler, event, data):
+        typing = get_flag(data, "typing")  # Check that handler marked with `typing` flag
+        if not typing:
+            return await handler(event, data)
+
+        async with ChatActionSender.typing(chat_id=event.chat.id):
+            return await handler(event, data)
+
+Use in utilities
+================
+
+For example you can collect all registered commands with handler description and then it can be used for generating commands help
+
+.. code-block:: python
+
+    def collect_commands(router: Router) -> Generator[Tuple[Command, str], None, None]:
+        for handler in router.message.handlers:
+            if "commands" not in handler.flags:  # ignore all handler without commands
+                continue
+            # the Command filter adds the flag with list of commands attached to the handler
+            for command in handler.flags["commands"]:
+                yield command, handler.callback.__doc__ or ""
+        # Recursively extract commands from nested routers
+        for sub_router in router.sub_routers:
+            yield from collect_commands(sub_router)