Automated PostgreSQL migration docs missing config in DB

[cwarnermm]

Context: https://hub.mattermost.com/private-core/pl/gny6xgcq3jbe88sairetdw49re

In our automated Postgres documentation we don't have the "configuration in database" paragraph, only in the manual migration docs, but is an important information. Do we want to add this?

https://docs.mattermost.com/deployment-guide/manual-postgres-migration.html#configuration-in-database

docs note: Potentially a content reuse opportunity.