dev/sg: spike approachability of sg.config.yaml

Created by: bobheadxi

sg.config.yaml is also nearing 1000 lines of configuration, which may become problematic - it will soon (and IMO already has) become rather daunting to change and contribute to.

We also have issues regarding running runsets of multiple teams/cross-domain (merging runsets), etc. that might contribute to solving this (if we make things more composable)

One idea is to have runsets be in code, leaving individual commands and tests in sg, so that merging strategies are easier to define