Set Prerelease to 'preview' for Az.DataTransfer module (#28625)

Author: VeryEarly

src/DataTransfer/DataTransfer/Az.DataTransfer.psd1

@@ -125,7 +125,7 @@ PrivateData = @{
 * Added commands for flow management'
 
         # Prerelease string of this module
-        # Prerelease = ''
+        Prerelease = 'preview'
 
         # Flag to indicate whether the module requires explicit user acceptance for install/update/save
         # RequireLicenseAcceptance = $false