docs(deployment): document cluster-sidecar architecture from the blog (#2092) * docs(deployment): add cluster-sidecar architecture header image Add the application-tier sidecar and distributed cluster diagram to the Cluster-Sidecar deployment architecture page. * docs(deployment): pull cluster-sidecar details from the architecture blog Reference the cluster-sidecar blog post and add the isolation model, latency tiers, snapshot topology, example Spicepods, and request path from that write-up.