Revamp the image build orchestration

The way images are defined currently is hard to read, tricky to modify and non-obvious. Rather than spreading out complexity all over, better concentrate it in the code, leaving the configuration readable.

After that, declare a dependency of SDK images on armhf development, to allow the future inclusion of the ospack into the SDK images as a part of T5423. This is done by adding a requires parameter, which will create several sub-stages to build the Arm image bits while building the SDK image.

This is currently being tested at: https://jenkins.apertis.org/job/playground/job/andrewsh/job/debos-images-build/lastBuild/flowGraphTable/

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• 3c2575f7 - Use a more verbose but more readable image definition format
• ffd8cb06 - Allow images to declare dependencies

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• a7e7e101 - 1 commit from branch master
• d8d45ee5 - Use a more verbose but more readable image definition format
• 7f93f003 - Allow images to declare dependencies

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• 79c8d311 - Use a more verbose but more readable image definition format
• ec61ef1a - Allow images to declare dependencies

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@em, other than that, any other comments?

Merging.

merged