add required values of approvalDescision to spec doc

[weshayutin]

Value:
"Unsupported value: "approved": supported values: "approve", "reject", "pending"" for field "spec.approvalDecision".

Doc:
NonAdminBackupStorageLocationRequestSpec defines the desired state of NonAdminBackupStorageLocationRequest

approvalDecision
string
approvalDecision is the decision of the cluster admin on the Requested NonAdminBackupStorageLocation creation.

Let's add "approve", "reject", "pending" to the spec doc

[weshayutin]

@mpryc FYI

[weshayutin]

openshift/oadp-operator#1642