unsupportedOverrides: for images is not accepted in OADP-1.3.x dpa

Description of problem:

  snapshotLocations:
    - velero:
        config:
          profile: default
          region: us-west-2
        provider: aws
  unsupportedOverrides:
    csiPluginImageFqin: quay.io/spampatt/velero-plugin-for-csi:fix-vsc-progress

User gets error:

```
Error "Unsupported value: map[string]interface {}{"awsPluginImageFqin":"quay.io/spampatt/velero-plugin-for-csi:fix-vsc-progress"}: supported values: "veleroImageFqin", "awsPluginImageFqin", "openshiftPluginImageFqin", "azurePluginImageFqin", "gcpPluginImageFqin", "csiPluginImageFqin", "resticRestoreImageFqin", "kubevirtPluginImageFqin", "operator-type"" for field "spec.unsupportedOverrides".
```

Expected Results:

A user should be able to override a container image used in the OADP deployment.

This is especially critical when working with customers and unreleased patches.