Convert tutorial/architecture.png into a Graphviz Dot Diagram for Easy Maintainance

[conallob]

https://prometheus.io/assets/tutorial/architecture.png is a helpful diagram, but it's a static image which has to be edited in an external tool and added to git.

For easier maintainability, it could use Graphviz' DOT language to define the image in text and use GitHub Actions to generate the resulting PNG image. This pattern is sometimes known as Diagrams-as-Code, alongside Docs-as-Code.

I'm happy to contribute a PR to both create the Diagrams-as-Code CI setup and define the new architecture diagram