[tutorial] Add abs tutorial

**Description of the tutorial**
... A tutorial for python built-in abs()

**Do you want to be assigned to work on this?**
(mark [x])
- [x] YES
- [ ] NO

**Optional: Any additional info you want to add**
...

Review the repository's existing beginner-friendly tutorials to find the appropriate structure and location for a new Python built-in tutorial. Add a tutorial explaining abs() for the target audience, and consider the work complete when it matches the surrounding tutorials and clearly teaches this function.

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