Look at docker image sizes

[surchs]

We recently reduced the query tool docker image size by more than 95% to 20 MB by using multi-stage builds. There may be other improvements for our other docker images. The benefit would be smaller resource footprint in deploying nodes, smaller transfer times on first pull or update, and probably other good things.

@mih shared this link (https://devopscube.com/reduce-docker-image-size/) with some ideas, let's collect more in this issue and see what we can implement easily: