python: Add .gitignore

This commit adds a Python .gitignore to the python/ directory, taking from the public domain gitignore file provided by GitHub¹.

Previously, I saw a __pycache__ in my git status which was not nice.

1. https://github.com/github/gitignore/blob/main/Python.gitignore ↩

requested review from @nickm

approved this merge request

CI failures seem to be timeout related.

mentioned in commit e76bd9fe

merged