Bring back Kaniko for building images

[Cervator]

When moving Jenkins I used the latest agents I had been working on coincidentally which were docker-in-docker based which isn't great for security. In the past we avoided that by using a Kaniko build agent to make the images. There's really no reason other than a bit of time to not just go back to that but time has this annoying thing about being finite and I'm trying to move on to some other priority stuff for the moment. To here a reminder goes!

Old main agent image building repo as of this writing: https://github.com/MovingBlocks/JenkinsAgentPrecachedJava