[3.x] Bot API 6.0 (#890)

* Base implementation

* Bump license

* Revert re-generated tests

* Fix tests, improved docs

* Remove TODO

* Removed unreachable code

* Changed type of `last_synchronization_error_date`

* Fixed wrongly cleaned code

docs/utils/web_app.rst

@@ -0,0 +1,55 @@
+======
+WebApз
+======
+
+Telegram Bot API 6.0 announces a revolution in the development of chatbots using WebApp feature.
+
+You can read more details on it in the official `blog <https://telegram.org/blog/notifications-bots#bot-revolution>`_
+and `documentation <https://core.telegram.org/bots/webapps>`_.
+
+`aiogram` implements simple utils to remove headache with the data validation from Telegram WebApp on the backend side.
+
+Usage
+=====
+
+For example from frontend you will pass :code:`application/x-www-form-urlencoded` POST request
+with :code:`_auth` field in body and wants to return User info inside response as :code:`application/json`
+
+.. code-block:: python
+
+    from aiogram.utils.web_app import safe_parse_webapp_init_data
+    from aiohttp.web_request import Request
+    from aiohttp.web_response import json_response
+
+    async def check_data_handler(request: Request):
+        bot: Bot = request.app["bot"]
+
+        data = await request.post()  # application/x-www-form-urlencoded
+        try:
+            data = safe_parse_webapp_init_data(token=bot.token, init_data=data["_auth"])
+        except ValueError:
+            return json_response({"ok": False, "err": "Unauthorized"}, status=401)
+        return json_response({"ok": True, "data": data.user.dict()})
+
+Functions
+=========
+
+.. autofunction:: aiogram.utils.web_app.check_webapp_signature
+
+.. autofunction:: aiogram.utils.web_app.parse_webapp_init_data
+
+.. autofunction:: aiogram.utils.web_app.safe_parse_webapp_init_data
+
+
+Types
+=====
+
+.. autoclass:: aiogram.utils.web_app.WebAppInitData
+    :members:
+    :member-order: bysource
+    :undoc-members: True
+
+.. autoclass:: aiogram.utils.web_app.WebAppUser
+    :members:
+    :member-order: bysource
+    :undoc-members: True