Is your feature request related to a problem? Please describe (👍 if you like this request)

Currently, Longhorn system backup doesn't backup volume data.

• If the volume in the system backup doesn't contain the last backup then that volume restored from the Longhorn system backup will not contain any data.
• The data in the volume last backup might not be the same data existing during the Longhorn system backup.

Describe the solution you'd like

Have a setting to allow to create volume backup during Longhorn system backup.

Describe alternatives you've considered

None

Additional context

None