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.

[jnewland]

Also requires the ProcMountType gate to be enabled via --feature-gates=ProcMountType=true.

[jnewland]

Seems like these requirements (and the use case) indicate that folks should be able to choose between running in privileged mode vs rootless mode if I'm able to make it work in any way.