Provide support for encrypted backups

Backups are currently stored in clear. When using a block storage provider, it would be useful to encrypt the backups before transfer. The encryption key could be stored in a secret. If a symmetric key is used, then backups can also be easily restored.

Acceptance criteria:

Part1:

• Investigate the and choose the options of encription.
• Create a POC.
• Define the initial model CRD.

Part2:

• Implement the encription options
• Update the documentation
• Implement the tests