Add "Run on Apify" button to doc code examples

- The result should match the behavior on the Crawlee website - see [apify/crawlee-python#1121](https://github.com/apify/crawlee-python/issues/1121).
- Idea: Update [example-code-runner-py](https://github.com/apify/example-code-runner-py) to include a flag for entering the Actor context.