docs: add new not_found feature

Author: heitorlessa

docs/core/event_handler/api_gateway.md

@@ -478,6 +478,48 @@ Similarly to [Query strings](#query-strings-and-payload), you can access headers
         return app.resolve(event, context)
     ```
 
+
+### Handling not found routes
+
+By default, Event Handler handles not found routes by simply returning 404 with `Not found` text.
+
+If you'd like to handle it any differently, you can use `not_found` decorator.
+
+```python
+from aws_lambda_powertools import Logger, Tracer
+from aws_lambda_powertools.logging import correlation_paths
+from aws_lambda_powertools.event_handler.api_gateway import ApiGatewayResolver, Response
+from aws_lambda_powertools.event_handler.exceptions import NotFoundError
+
+tracer = Tracer()
+logger = Logger()
+app = ApiGatewayResolver()
+
+@app.not_found
+@tracer.capture_method
+def handle_not_found_errors(exc: NotFoundError) -> Response:
+    # Return 418 upon 404 errors
+    logger.info(f"Not found route: {app.current_event.path}")
+    return Response(status_code=418, content_type=content_types.TEXT_PLAIN, body="I'm a teapot!")
+
+
+@app.get("/catch/me/if/you/can")
+@tracer.capture_method
+def catch_me_if_you_can():
+    return {"message": "oh hey"}
+
+# You can continue to use other utilities just as before
+@logger.inject_lambda_context(correlation_id_path=correlation_paths.API_GATEWAY_REST)
+@tracer.capture_lambda_handler
+def lambda_handler(event, context):
+    return app.resolve(event, context)
+```
+
+
+### Exception handling
+
+
+
 ### Raising HTTP errors
 
 You can easily raise any HTTP Error back to the client using `ServiceError` exception.