Missing docker image size optimization and tests

[jerome-benoit]

• tools not needing to be shipped in the image like gnupg are not cleaned up
• changes to image are put in different layers of the multistage build
• several Dockerfiles where only one is needed
• no architecture platform support check
• no smoke test

You can find a properly optimized Dockerfile here: https://github.tools.sap/E-Mobility/mbt-docker/blob/main/Dockerfile with a section to install SAP machine with image size optimization.
And a PR showing how to reuse the same Dockerfile to generate images for different version: https://github.tools.sap/E-Mobility/mbt-docker/pull/8

[jerome-benoit]

The example repo now archived with latest changes has moved here: https://git.piment-noir.org/?p=mbt-docker.git;a=summary