First iteration of service maturity model
I've created the first iteration of this model, following from &382 (closed). Closes: #750 (closed)
Caveats:
- it's probably not the best place for it to live, but we can figure that out later
- it's probably not the best format, but the content is more important for this round
The text is from the spreadsheet linked in the description of the epic, and I started looking at Sidekiq to see how the model holds up. Sidekiq meets more of these criteria, but I wasn't sure how to show that without adding a lot of writing.