package gardenlinux releases into an oci

[gehoern]

oci supports now oci artifacts:

• originally in oci you could only publish layers each layer was a tar containing the data of the relevant option (nginx consited of the layer nginx and debian -> nginx had a metadata refering to the layers see https://dlorenc.medium.com/oci-artifacts-explained-8f4a77945c13 -> this had certain impacts: e.g. if you had a debian layer this was automatically deduplicated because it was referenced via a hash and therefore after an update of nginx to the next debian - the dependency to the old stuff was removed)
• now you can store anything as a "layer" or better artifacts. that means we could now release our different flavours as an oci artifact and make sure that descriptive stuff like (logs, os-release, contend description ...) goes into a standard layer but anything that is binary (vmlinuz, initrd, boot disk) goes as an artifact (implicit we have only one version of the kernel everything else is auto deduplicated). So we can boot out of any oci registry.

this is a proposal for a tool to use all this. we need to orchestrate. https://github.com/onmetal/onmetal-image