Enable scheduled snapshots for instances

Problem/Justification
Issue is that VM/LXC instance cannot be rolled back since you cannot select the respective volumes to be included in snapshot tasks (at least not from what i’ve found). This would be super helpful in order to reverse any changes made or data accidentally deleted or an failing update. Especially since it doesn’t seem possible to directly mount datasets to a VM yet.

Impact
Users can easily create schedules snapshot tasks for instances both VM and LXC containers in order to protect them.

User Story
As a User I’d like to be able to select instance volumes when creating scheduled snapshot tasks in order to protect these instances.