GH building action followups

[kkourt]

Followups items for #23

• write a GH action that pushes tags whenever something is pushed in main or in other branches (e.g., v0.1). The idea is to use the tags under versions/ that are generated from the build action to tag these versions.
• avoid building root images every time. We should build root images only when the image configuration changes. We can have an actions that creates a file with string to a /etc/lvh-version version in the configuration for only triggering rebuilds by modifying the string.
• write some tests for the resulting images. We can, for example, ensure that all the images exist in the query repo and/or boot a simple VM to check basic functionality such as ssh/DNS/etc.
• Add an expiration date to the images we generate for PRs. Currently, we tag every image so that the images will not go away. It would be good if we could attach an expiration date to these tags (see https://access.redhat.com/documentation/en-us/red_hat_quay/3/html/use_red_hat_quay/working_with_tags). To do that, however, we would need a way to tag images that we use so that they persist after the expiration date. (see point 1).
• have a way for users to easily identify whether the images are build (e.g., a comment in the PR with the GH actions link or some label)