add Legend omnibus Docker setup

[akphi]

Essentially, this is Legend in a box + Gitlab plus some quality-of-life improvements for the config. It's a zero-setup/zero-config uber/omnibus starter for the Legend stack, so if we publish this image to Dockerhub, everyone can start Legend Studio with one command. For example, I have published one such omnibus image to Dockerhub, try the following to test

docker run --platform=linux/amd64 -it -p 6100:6100 -p 6300:6300 -p 9000:9000 -p 6900:6900 -p 6901:6901 -p 6902:6902 blacksteed232/legend-omnibus:beta