Reduce privileges granted to docker container

[jnewland]

Background

• The docker:stable-dind-rootless container has a few requirements that aren't satisfied by all clusters today.
• https://blog.jessfraz.com/post/building-container-images-securely-on-kubernetes/ has background on all of the rad patches that may possibly enabling running the rootless dind container without --privileged.
• This blog post has some additional historical background.
• This one is a bit more recent.