Backup persistence.conf before modifying it in t-p-s
… as suggested in #10976 (comment 64529).
Even without the restore code suggested there, saving a backup should already be a net win:
- for users who might notice the “.bak” file and recover themselves
- for help desk when they help users recover from #10976 (closed)
- for me when I get debugging data about #10976 (closed) (depending on the mtime of the backup file, I’ll be able to tell for sure if t-p-s was used at all recently, regardless of what users remember: nothing else modifies this backup file).
Feature Branch: bugfix/16461-lost-persistence-config, persistence-setup:bugfix/16461-lost-persistence-config
Parent Task: #10976 (closed)