Migrate away from uw-saml-poetry base image for improved clarity and independence

[soufianerafik]

Context: The current Dockerfile uses the shared base image ghcr.io/uwit-iam/uw-saml-poetry, which is now no longer maintained and is being removed from the shared docker repo as part of a cleanup effort.

This image was originally helpful for bootstrapping Poetry and preloading uw-saml-python, but it's become a source of hidden dependencies and fragility.

Why we should move off it?

• Not maintained: The uw-saml-poetry image hasn’t been updated in years and won’t get any future updates or fixes.
• Too tightly coupled: It bundles both Poetry setup and app-specific stuff, so changing one part means dealing with the whole image.
• Less flexible: It's better if each repo owns its own setup so we’re not tied to shared images for basic tools like Poetry.

The base image does a lot under the hood, making it harder to trace or customize how dependencies are installed.

Recommendation:

• Going forward, I recommend we rely on the python base images with Poetry installed via pipx, which are maintained in a more flexible and versioned build matrix.

This is how we currently handle it in Identity.UW: docker/identity-uw.dockerfile