Add Distribution project overview and mermaid diagrams
There was a discussion of how GitLab will be deployed in the multi-large working group. A request was raised to document various deployment technologies and in-house developed tools to deploy GitLab and the relations between these technologies https://docs.google.com/document/d/1dbJZNAiTVvwJ9ICu10FpxP9AaAVDXDVkATmpzSONztE/edit#bookmark=id.btgq0e3la6yf.