Support new backup configuration in SGCluster on the web console

When #862 (closed) is done, apply the following proposed spec on the SGCluster CRD:

spec:
  configurations:
    sgBackupConfig: <string> # this does not change bu will be deprecated and mutually exclusive with `backups` field.
    backups:
    - path: <string>
      compression: <string>
      cronSchedule: <string>
      performance:
        maxDiskBandwitdh: <integer>
        maxNetworkBandwitdh: <integer>
        uploadDiskConcurrency: <integer>
      retention: <integer>
      sgObjectStorage: <string> # name of an SGObjectStorage in the same namespace

Implementation plan:

• Detail the CRUD model for this CRD.

Acceptance criteria:

• Implement the CRUD.
• Implement some tests.