namespace object should always been backed up if any objects in it are backed up

[27149chen]

What steps did you take and what happened:

1. Backup some resources in a namespace which match a label
2. The namespace resource is not backed up because it does not have such labels

What did you expect to happen:
namespace is backed up

The following information will help us better understand what's going on:

If you are using velero v1.7.0+:
Please use velero debug --backup <backupname> --restore <restorename> to generate the support bundle, and attach to this issue, more options please refer to velero debug --help

If you are using earlier versions:
Please provide the output of the following commands (Pasting long output into a GitHub gist or other pastebin is fine.)

• kubectl logs deployment/velero -n velero
• velero backup describe <backupname> or kubectl get backup/<backupname> -n velero -o yaml
• velero backup logs <backupname>
• velero restore describe <restorename> or kubectl get restore/<restorename> -n velero -o yaml
• velero restore logs <restorename>

Anything else you would like to add:

Environment:

• Velero version (use velero version):
• Velero features (use velero client config get features):
• Kubernetes version (use kubectl version):
• Kubernetes installer & version:
• Cloud provider or hardware configuration:
• OS (e.g. from /etc/os-release):

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[sseago]

Yes, I think this makes sense to add. In some cases, metadata on the namespace resource is required for included applications to work properly (i.e. UID/GID range annotations on the namespace in some clusters).