By default, ONCE pauses the application container when taking a backup.
This guarantees a consistent snapshot of the data, but for a large
installation and/or a slow destination path (like a network mount), that
pause could be a bit disruptive to live traffic.
But ONCE also support a pause-free path: if a `pre-backup` hook is
present in the container, ONCE will run that and skip the pause. So by
supplying necessary hooks, we can avoid any disruption from backups.
- `pre-backup` runs the existing script/admin/prepare-backup, which uses
SQLite's online backup API to get a consistent snapshop.
- `post-restore` moves our snaphotted file back into place, and removes
the orphaned sidecar files
Kevin McConnell