[backplane-2.3] exclude managedclusterset crd from backup

[openshift-cherrypick-robot]

This is an automated cherry-pick of #67

/assign zhujian7

[zhujian7]

/hold

[zhujian7]

/lgtm

[zhujian7]

/approve

[openshift-ci]

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[zhujian7]

/cc @zhiweiyin318 need your approve

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