Use pydantic for accessing Ansible facts

[ckunki]

The AI-Lab build architecture uses Ansible facts set in general_setup_tasks.yml to define main configuration options in a single place and to pass these configurations to all related build steps.

When create_image.py runs Ansible, it also retrieves the facts afterward, and uses them to configure the Dockerfile and to parameterize its entry point in entrypoint.py.

Improvements and additions to the AI-Lab added more and more Ansible facts. File entrypoint.py and related tests already implemented some helper functions to handle Ansible facts more conveniently.

The current ticket therefore proposes to use pydantic to make it even easier to handle Ansible facts.