Command to publish assets to OCI registry

[janiskemper]

/kind feature

Describe the solution you'd like
A new command "publish" that can be used to publish assets to an OCI registry. This is the equivalent to what we do currently in "create" where we store the assets in a local output folder. Instead of doing that, we want to upload them.

This feature is the counterpart of SovereignCloudStack/cluster-stack-operator#157