[BUG] transfer-pvc: validate/default destination storage class before creating the destination PVC

[nachandr]

What version of crane are you running, and what are your clutsters+platform
latest on main branch on OCP clusters

Summary
crane transfer-pvc copies the source PVC's storageClassName onto the
destination PVC and only overrides it when --dest-storage-class is passed. When
the destination cluster has no storage class of that name — always the case across
providers (e.g. AWS→GCP), where class names don't overlap — the destination PVC is
created but never binds, the mover pod stays Pending, and the run fails after a
5-minute pod-start timeout with an error that gives no indication of the cause.

There is no pre-flight validation that the destination storage class actually exists
on the destination cluster.

I believe this is applicable to both direct and indirect migration.

Steps to Reproduce

1. Create a source PVC mysql-data on gp3-csi with some data, in a namespace
   present on both clusters.

2. Run an indirect transfer without --dest-storage-class:

   crane transfer-pvc \
     --source-context      <src> \
     --destination-context <tgt> \
     --pvc-name            mysql-data \
     --pvc-namespace       indirect-rclone-secret-mysql:indirect-rclone-secret-mysql \
     --cloud-storage       remote:<bucket> \
     --rclone-config-secret <secret>

Actual Result
Upload succeeds; download times out and the run aborts:

[3/6] Uploading data to cloud storage ... ok
[4/6] Downloading data from cloud storage ...
[6/6] Cleaning up transfer pods ... ok
Error: download pod failed: timed out waiting for pod
indirect-rclone-secret-mysql/rclone-download-mysql-data to start:
context deadline exceeded

What did you expect to happen?
Before creating the destination PVC or any pod, crane should either:

• Validate + fail fast, with a clear message naming the missing storage class and
  listing valid alternatives, or
• Default to the destination cluster's default storage class when the copied
  source class is absent, logging the substitution.

Please include any relevant logs or errors