[Feature Request] Set base python version based on asdf set python order #208

I think it would be helpful to set the base Python version (invoked when running python) based on the order Python versions are set. asdf does work as expected when using the more specific Python versions (python3.12, etc.), but I find it convenient to be able to type just python and get the version I want to use most often. I don't have pyenv installed anymore, but if I remember correctly, it has this behavior.

Current behavior:

❯ asdf set -u python 3.12.7 3.9.20
❯ python --version
Python 3.9.20

Desired behavior:

❯ asdf set -u python 3.12.7 3.9.20
❯ python --version
Python 3.12.7