How to do a complete backup and restore of Central

Whole machine backups are nice, but if someone wants to backup just the key things, what should they do?

* Central folder with any git changes
* Any OS changes (e.g., daemon.json)
* Data
* Option 1: Docker data folder
* Option 2: Central Postgres DB, Enketo Redis DB (main and cache), secrets values

Start from the issue's list of Central files, OS changes, Docker data, PostgreSQL, Redis, and secrets, and organize the required backup and restore steps. No file or test is named; done means the documentation covers both data-storage options and the listed configuration and secret values without relying on a whole-machine backup.

Written by the indexing model from the issue text.