Clarify GitLab CI runners production architecture
This is currently a blind spot in the whole production as it has been maintained by the CI team.
We need to have an architecture diagram explaining how things are built in DigitalOcean to make informed decisions on how things are going to be executed when we move to GCP, and to even decide if we are going to move the CI fleet to GCP at all.
I'm assigning this issue to @ayufan and @nolith as they are the ones listed in https://about.gitlab.com/handbook/engineering/projects/#gitlab-runner