Update .gitignore: exclude .env files and pyenv .python-version

[GR360RY]

1. It is common to keep environment variables in either .env or .envrc files in the project root folder. To avoid accidental secrets leak, exclude .env files.
2. To support kickstart files validation and syntax highlighting pykickstart python package can be used together with "Kickstart Language Support" plugin for VScode. If python environment is managed with pyenv, make sure to exclude .python-version which is always local for user's environment.