Added AdminFilter and example of its usage

examples/admin_filter_example.py

@@ -0,0 +1,28 @@
+import logging
+
+from aiogram import Bot, Dispatcher, types, executor
+
+API_TOKEN = 'API TOKEN HERE'
+
+logging.basicConfig(level=logging.DEBUG)
+
+bot = Bot(token=API_TOKEN)
+dp = Dispatcher(bot=bot)
+
+chat_id = -1001241113577
+
+
+# checks specified chat
+@dp.message_handler(admin_chat_id=chat_id)
+async def handler(msg: types.Message):
+    await msg.reply(f"You are an admin of the chat '{chat_id}'", reply=False)
+
+
+# checks current chat
+@dp.message_handler(admin_current_chat=True)
+async def handler(msg: types.Message):
+    await msg.reply("You are an admin of the current chat!", reply=False)
+
+
+if __name__ == '__main__':
+    executor.start_polling(dp)