update architecture docs

[rokroskar]

We should go through our architecture docs and update the diagrams and/or descriptions to make sure they match current reality.

• main architecture diagram chore: update arch docs and add mermaid #2566
• notebook service / amalthea (@SwissDataScienceCenter/renku-notebooks-maintainers) chore(docs): add sequence diagram to readme renku-notebooks#1047
• core service (cc @SwissDataScienceCenter/renku-python-maintainers)
• graph service (cc @SwissDataScienceCenter/renku-graph-maintainers)
• gateway (cc @SwissDataScienceCenter/renku-gateway-maintainers)
• diagram to explain the k8s layer components

See also #2492 which is asking for a more user-friendly version of the high-level architecture diagram.

[olevski]

@rokroskar what do you mean by

diagram to explain the k8s layer components

Is this more related to how amalthea handles things? Or just the general order of the renku helm deployment in k8s?

[rokroskar]

I meant all the supporting k8s infra like cert-manager, ingress, load-balancer etc.