[k8s][vm] Restructure information about primary vs. leader unit #108
Description
Currently, the Scale your cluster guide has a section clarifying the difference between primary and units, and how to determine them. This is a somewhat hidden/unexpected place, and we've received user feedback that this information was not found when needed.
Reconsider where this information should live, and what other pages/contexts should link to it. (i.e. other situations where actions need to be run on the primary/leader)