Create a file `shopping.py` that contains a function `clean_list` which takes in a list of strings and performs the following operations on each list item:
- Removes all spaces before and after (but not between words).
- Capitalizes the first letter (first letter only, other ones should be to lowercase).
- Adds its index number before a separator `x/ `.
- An empty list as input should return an empty list as output.
- And don't forget the milk !!!! (add it at the end of the list if missing).
### Usage
Here is an example of how to use the clean_list function: