Port Raudi to python_on_whales

[frost19k]

This PR replaces the docker-py library with python_on_whales.

Justification:

• docker-py does not (and possibly, will not) support Buildkit. Issue #2230
• Not having access to BuildKit means that raudi.py is restricted to using only the simplest Dockerfiles.
• For full details regarding the advatages of BuildKit please refer to the blog post.
• Additionally, since python_on_whales is essentially a wrapper around Docker CLI, it is a lot simpler to implement & maintain ( for e.g. check_if_docker_image_exists_local() in helper.py is now just one line! )

Changes:

• I've updated build() & push() in raudi.py with the new syntax. I've tested the build() function & confirmed that it works correctly (see Add "dev" branch for experimental features #20) - but I have not tested push().
• In helper.py I updated the code in check_if_docker_image_exists_local() & check_if_container_runs(). Please mind my comments in the latter.
• While I added python_on_whales in requirements.txt I did not remove docker. This is merely to facilitate debugging & it should be removed before merging into main.

As far as I'm aware - that should be everything. Apologies if I missed something.

[thelicato]

Thank you very much! We will test everything in the next couple days and if everything is ok we will merge it into main.