Add proposal for snapshot support

[afritzler]

Proposed Changes

• Introduce Snapshot and SnapshotClass resources to allow users to take point-in-time snapshots of the content of a Volume
• Enhance the Volume resource to include a dataSource field for restoring data from a snapshot
• Improve data protection and disaster recovery capabilities
• Provide support for different types of snapshots based on VolumePool capabilities
• The proposal does not modify existing VolumePool resources
• The Snapshot resource is not designed to provide a complete backup or archival solution for Volumes
• The actual creation and readiness of a snapshot can depend on various factors such as Volume size, VolumePool capabilities, and infrastructure performance
• The Snapshot resource and restoration path are meant to be additional tools in the data protection toolbox, not to replace existing comprehensive disaster recovery and data protection solutions

Fixes #801

[balpert89]

We have discussed the PR internally and do not see a problem with going forward as-is. We do not recommend going forward with the mentioned alternatives as its either off-loading significant portions to the user (3rd party provider), complicate interaction (storage provider APIs) or restrict flexibility (adding to Volume).