Added a section on Dependency Injection technology in documentation (#1253)

* Added a section on Dependency Injection technology in documentation

* Added changelog

* Edited comments & titles

examples/context_addition_from_filter.py

@@ -0,0 +1,33 @@
+from typing import Any, Dict, Optional, Union
+
+from aiogram import Router
+from aiogram.filters import Filter
+from aiogram.types import Message, User
+
+
+router = Router(name=__name__)
+
+
+class HelloFilter(Filter):
+    def __init__(self, name: Optional[str] = None) -> None:
+        self.name = name
+
+    async def __call__(
+        self,
+        message: Message,
+        event_from_user: User
+        # Filters also can accept keyword parameters like in handlers
+    ) -> Union[bool, Dict[str, Any]]:
+        if message.text.casefold() == "hello":
+            # Returning a dictionary that will update the context data
+            return {"name": event_from_user.mention_html(name=self.name)}
+        return False
+
+
+@router.message(HelloFilter())
+async def my_handler(
+    message: Message, name: str  # Now we can accept "name" as named parameter
+) -> Any:
+    return message.answer(
+        "Hello, {name}!".format(name=name)
+    )