This PR updates the Log File Rotation module for openSUSE Leap 16's split `/usr/etc` and `/etc` configuration model.
- Select the local main configuration when present, otherwise use the vendor configuration.
- Recursively merge vendor and local drop-ins using the same precedence as `logrotate-all`.
- Display vendor configurations while keeping `/usr/etc` read-only.
- Copy vendor files into matching `/etc` overrides before editing or deleting them.
- Preserve empty overrides so deleted vendor rotations remain disabled.
- Use the openSUSE wrapper for scheduled rotation and the effective configuration set for forced rotation.
- Keep behavior unchanged on distributions that do not enable the vendor overlay.
Includes regression coverage for selection, precedence, copy-on-write, deletion, scheduling, backups, and protection against direct vendor writes.
Closes [#2682](https://github.com/webmin/webmin/issues/2682).
