Upgrade CloudStack controlPlaneConfigurations.machineGroupRef.name field failed

[jiayiwang7]

For Cloudstack, upgrade of controlPlaneConfigurations.machineGroupRef.name field fails with below error

panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x10 pc=0x31e954c]

goroutine 1 [running]:
github.com/aws/eks-anywhere/pkg/providers/cloudstack.(*cloudstackProvider).validateMachineConfigNameUniqueness(0xc000597e50?, {0x46639d0?, 0xc000132008?}, {0xc000544a10, 0xe}, 0xa?)
        /Users/pjshah/workspace/eks-anywhere/pkg/providers/cloudstack/cloudstack.go:1359 +0x4c
github.com/aws/eks-anywhere/pkg/providers/cloudstack.(*cloudstackProvider).validateMachineConfigsNameUniqueness(0xc00081c200, {0x46639d0, 0xc000132008}, 0xc0007a4a00?, 0xc0007a4a00)

Upon debugging, it looks it fails at https://github.com/aws/eks-anywhere/blob/main/pkg/providers/cloudstack/cloudstack.go#L1325 line. clusterSpec.Cluster.GetNamespace() throws an error and thus cluster upgrade fails with panic.