Expand Cloud Native Hybrid build documentation

Problem

Existing Cloud Native Hybrid documentation doesn't outline specific steps that customer should do to build an environment.

• Omnibus secrets should be migrated to k8s, related documentation https://docs.gitlab.com/charts/installation/migration/package_to_helm.html
• Order of components installation
• Cross-link with https://docs.gitlab.com/charts/installation/#configure-the-helm-chart-to-use-external-stateful-data

Goal

Document high-level steps for cloud native build at Reference Architecture docs.