Initializes asdf, installing it using git if not installed yet. Unlike the original zimfw/asdf this version does not bypass the shims if direnv plugin is detected.
The path of ASDF_DIR, where asdf is installed, is checked among the usual
directories created by Homebrew or Pacman, or the default ${HOME}/.asdf. You
can define ASDF_DIR, before where this module is initialized, to customize
it's path:
ASDF_DIR=/path/to/asdf_dir