Document supported cloud-storage providers for indirect PVC transfer

[stillalearner]

Summary

The crane transfer-pvc --cloud-storage documentation should explicitly state which storage providers are supported by the transfer image currently shipped for indirect PVC migration.

Crane delegates indirect transfer to rclone. Although Crane accepts a generic rclone remote path, actual provider support is determined by the rclone backends compiled into the transfer image.

The current transfer image includes the rclone s3 backend. Therefore, supported object storage is any service usable through rclone’s S3 backend.

Storage provider	Supported now	rclone config	--cloud-storage example
AWS S3	Yes	type = s3 provider = AWS	remote:mybucket
Google Cloud Storage via S3 API	Yes	type = s3 provider = GCS endpoint = https://storage.googleapis.com GCS HMAC credentials	remote:mybucket
MinIO	Yes	type = s3 provider = Minio endpoint = https://<minio-endpoint>	remote:mybucket
Other S3-compatible object storage	Yes, if rclone S3-compatible	type = s3 Provider/endpoint appropriate for the service	remote:mybucket
Azure Blob Storage	No currently	type = azureblob backend is not compiled into the image	N/A
Native GCS backend	No currently	type = gcs backend is not compiled into the image	N/A
Azure Files / NFS / EBS / GCE PD	No	Not object-storage remotes for indirect transfer	N/A

Documentation changes requested

1. Replace or clarify “S3-compatible cloud storage” in transfer-pvc documentation.
2. Add the supported-provider table above.
3. Document the required --cloud-storage format.
4. State that a raw bucket name, s3:// URL, gs:// URL, or bucket ARN is not a valid value.
5. State that both source and destination transfer Pods need access to the same configured object-storage path, including list/read/write/delete permissions.

[aufi]

Thanks for creating this issue, it has a great fit to xKS migration support topic 👍