Add Velero CLI to Sylva-toolbox Extended Image

Description

This issue tracks the addition of the Velero CLI to the Sylva-toolbox extended Docker image.

• Installing Velero CLI in the extended toolbox image
• Updating Dockerfile-extended

Benefits

• Users can now interact with Velero directly from the Sylva-toolbox image.
• Facilitates testing and automation of Kubernetes backup/restore workflows.