feat(python): Support Python builds using `mbtci` Docker images

[silvestre]

Description

This change keeps python3 installed and adds python3-pip and python3-dev, so that the resulting image can be used in Piper-based pipelines to build Python apps:

• pip might be needed for vendoring the dependencies, during the mtaBuild, so that the resulting MTA is self-contained when deployed in air-gapped CF.
• FOSS scanning using detectExecuteScan also relies on the pip tool being available.

I have not yet touched the tests, as I wanted to get the discussion rolling if this is a change you would likely merge. I believe it would make sense to fully support Python in your Docker images as it is an enterprise-supported language when targeting SAP BTP, Cloud Foundry environment

In case you agree, I can adapt the tests as well.

Checklist

• [ ] Code compiles correctly
• [ ] Relevant tests were added (unit / contract / integration)
• [ ] Relevant logs were added
• [ ] Formatting and linting run locally successfully
• [ ] All tests pass
• [ ] UA review
• [ ] Design is documented
• [ ] Extended the README / documentation, if necessary
• [ ] Open source is approved