feat: render CRD additionalPrinterColumns for custom resources

[DepravityDemo]

Summary

kubectl get <custom-resource> against an sbctl-served bundle only showed
NAME and AGE, and -o wide added nothing — even though the bundle contains
the resource's CustomResourceDefinition with additionalPrinterColumns. A
live apiserver renders those columns; sbctl did not.

This happens because custom resources are served as unstructured objects and
rendered with the built-in table generator (printersinternal.AddHandlers),
which only knows core/apps/batch types. Unknown types fall back to a generic
NAME/AGE table.

Change

toTable now detects unstructured objects and, when the bundle ships the
matching CRD, builds a table with the CRD's additionalPrinterColumns via the
apiextensions tableconvertor. It falls back to the existing built-in table
when no CRD matches or it declares no extra columns, so all existing behavior is
preserved.

• New helper crdPrinterColumns reads custom-resource-definitions.json and
  matches the request's group/version/resource.
• toTable becomes a handler method so it can reach clusterData.
• Only v1 CRDs are handled; v1beta1 bundles fall through unchanged.

Before

$ kubectl get pg -A
NAMESPACE   NAME               AGE
default     job-d810lpwk17on   23h

After

$ kubectl get pg -A
NAMESPACE   NAME               STATUS    MINMEMBER   RUNNINGS   AGE
default     job-d810lpwk17on   Running   1           1          23h

$ kubectl get pg -A -o wide
NAMESPACE   NAME               STATUS    MINMEMBER   RUNNINGS   AGE   QUEUE
default     job-d810lpwk17on   Running   1           1          23h   aihcq-qitkz4auspzc

Test plan

• Added integration test tests/backupstoragelocations_test.go using the
  existing velero.io BackupStorageLocation CRD fixture; asserts the
  Phase / Last Validated / Default columns are rendered.
• go test ./tests/... passes (existing pods/configmaps specs unaffected).
• gofmt, go vet, and golangci-lint clean on the changed code.
• Manually verified against a real Volcano PodGroup support bundle.