storage/transfermanager: transfermanager library still in preview

[sambhav-jain-16]

Is your feature request related to a problem? Please describe.

Hi team, any plans to make transfermanager no longer in preview?

google-cloud-go/storage/transfermanager/doc.go

Lines 25 to 27 in 2b08b5d

	NOTE: This package is in preview. It is not stable, and is likely to change.
	*/
	package transfermanager // import "cloud.google.com/go/storage/transfermanager"

Describe the solution you'd like

Make transfermanager GA

Describe alternatives you've considered

Additional context

We use TransferManager for downloading blobs from the GCS bucket, but there have been recent concerns regarding the package in preview.

[cpriti-os]

Yes there are plans to take this out of preview, but we do not have plans/resources to prioritize it in the next few months.