Optimize python build time

[cbeauchesne]

Description

• Use python-slim as base image
• use pre-build base image for python weblogs

See #562

Motivation

Build time !

Reviewer checklist

• If this PR modifies anything else than strictly the default scenario, then add the run-all-scenarios label (more info).
• CI is green
  • If not, failing jobs are not related to this change (and you are 100% sure about this statement)

Workflow

1. ⚠️⚠️ Create your PR as draft
2. Follow the style guidelines of this project (See how to easily lint the code)
3. Work on you PR until the CI passes (if something not related to your task is failing, you can ignore it)
4. Mark it as ready for review

Once your PR is reviewed, you can merge it! ❤️

[smola]

It seems the base images wouldn't be built and pushed by CI on merges. What would be the workflow when there are changes to the base images?

[cbeauchesne]

They are actually very stable. For now, we'll build/push them locally if needed.

If it turns out that it happen more often than I anticpate, it will be something like an optionnal job triggered by a label.