Add a section about hardening image at build time using kiwi

[diconico07]

Details how to build a hardened image using kiwi, the example tailoring file is taken from Sylva Image building with some light adaptation.

[hardys]

lgtm - thanks!

I wonder if we should consider adding the configuration described here to the kiwi builder container in future so that less copying and copy/paste configuration is needed but this seems OK as a starting point.

[diconico07]

I wondered the same, but IIRC we are taking those verbatim from the SL Micro build process, so any modification would make maintenance harder (unless we find a way to get those modifications to happen in the "upstream" build files).

[hardys]

I wondered the same, but IIRC we are taking those verbatim from the SL Micro build process, so any modification would make maintenance harder (unless we find a way to get those modifications to happen in the "upstream" build files).

Perhaps we could consider a patching/sed workflow in the image build, but not blocking on that - this seems fine as a first step and we can consider if we can make the process easier in a future iteration