nuageinit: use lyaml to parse yaml files

This fixes case where vendors or cloudinit consumers are using all
features from yaml.

KDE is using reference for its CI for example.
lima-vm uses syntax for which our previous yaml.lua has bug in the
parser (https://github.com/lima-vm/lima/issues/1508)

(cherry picked from commit 40dafa08b2e7a04d2662b601ef89b48132c1b6c1)