docs: Correct the serviceAccount schema descriptions

[lfrancke]

Fixing the documentation for when the related templating changes (see below) land.

Merge order

This should probably land after all the ones below and after templating has rolled out...but in reality it doesn't matter too much as long as everything is merged before 26.11

The full chain:

1. fix: Make serviceAccount.name and serviceAccount.create work listener-operator#418 and fix: Make serviceAccount.name and serviceAccount.create work secret-operator#736
2. fix: Port the serviceAccount.name/create fix into the template operator-templating#634, Hive 4 clarifications #635, chore: Bump zookeeper version for 25.11.0 #637
3. A templating run
4. this PR