Provide a simple way to determine Liberty version

[leochr]

Labels version and org.opencontainers.image.version are set on the Liberty images. But this could be overridden by application images (getting-started Liberty app does that). Create a unique label to specify the version of Liberty runtime, so it can be easily retrieved from the image metadata.

Suggest to add these:

• liberty.version (so it's common for both OL and WL)
• com.ibm.websphere.liberty.version (for WL)
• io.openliberty.version (for OL)

Users can use skopeo inspect command to retrieve Liberty runtime version. The goal is to determine the version without running the image. Podman/docker inspect could be used as well, but that requires the image to be pulled.

• Delivered to WebSphere Liberty
• Delivered to Open Liberty