- Merges the "Backups" section from production/maintain-secure-upgrade.md
with existing "Backups" section in production/export-and-import.md.
- Cleans up and makes content more clear/explicit.
- Adds short missing section on how to use wal-e configuration.
- Removes a lot of previously duplicate text explaining the difference between
the tools.
- Various textual tweaks by tabbott.
Fixes#13184 and resolves#293.
This lets us handle directly in our tooling the user experience that
we document for exporting a realm with member consent (before, it
required unpleasant manual work).