Introduce poetry python package management tool

Types of changes

New feature
Refactoring
Breaking change (any change that would cause existing functionality to not work as expected)
Documentation Update

Description

Per our discussion on MM, we will poetry to manage ubuntu-server-netboot as a python package for the distribution purpose later, and development of test cases.

Checklist:

[ ] Add test cases to all the changes you introduce
[ ] Run poetry run pytest locally to ensure all linter checks pass
[ ] Update the documentation if necessary

Steps to Test This Pull Request

Follow the updated README and it should generate the same content of grub.cfg as what its previous codebase does. What the only change a user will be aware of is the command name migrating to ubuntu-server-netboot from ubuntu-server-netboot.py.

Expected behavior

grub.cfg is the same. No regression of grub.cfg.

Additional context

After we land this pull request, I will build the python package and update the README to show how to install ubuntu-server-netboot as a python package from PyPI or as a deb package from PPA directly. We will address this issue in more details later.

dannf / ubuntu-server-netboot