New-DcnImage uses $Credential for testing access, instead of $DestinateionCredential

[blitzmann]

https://github.com/dataplat/dbaclone/blob/1bf77597166f86a7ce741984d40fab8f54b73e5c/functions/image/New-DcnImage.ps1#L238-L257

These commands use $Credential, however they are never defined., I believe it's supposed to be $DestinationCredential. This is currently preventing us from creating a new image on our build server and passing in admin credentials, because it's not actually using them.