SnowBallEdge EKS-A Upgrade fails for Instance Type Upgrade.

**What happened**:

SnowBallEdge EKS-A Upgrade fails for Instance Type Upgrade. I tried to upgrade from `large` instance to `2xlarge` instance for nodes and the upgrade fails with below errors

```
2023-05-09T15:53:23.575Z V6 Executing command {"cmd": "/usr/bin/docker rm -f -v eksa_1683647549800094637"}
panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x110 pc=0x2a2604c]

goroutine 1 [running]:
github.com/aws/eks-anywhere/pkg/providers/snow.(*SnowProvider).EnvMap(0x2dc0e40?, 0xc000570f80)
github.com/aws/eks-anywhere/pkg/providers/snow/snow.go:197 +0x4c
github.com/aws/eks-anywhere/pkg/executables.(*Clusterctl).InstallEtcdadmProviders(0xc00037bc40, {0x3a65990, 0xc000126000}, 0x1c?, 0xc00041a330, {0x3a73eb0, 0xc0002eb860?}, {0xc0001415e0, 0x2, 0x2})
github.com/aws/eks-anywhere/pkg/executables/clusterctl.go:422 +0x2df
github.com/aws/eks-anywhere/pkg/clusterapi.(*Installer).EnsureEtcdProvidersInstallation(0xc00056e618, {0x3a65990, 0xc000126000}, 0xc00041a330, {0x3a73eb0, 0xc0002eb860}, 0xc000570f80)
github.com/aws/eks-anywhere/pkg/clusterapi/installer.go:49 +0x2bc
github.com/aws/eks-anywhere/pkg/workflows.(*ensureEtcdCAPIComponentsExistTask).Run(0xc000548e80?, {0x3a65990, 0xc000126000}, 0xc0001320f0)
github.com/aws/eks-anywhere/pkg/workflows/upgrade.go:206 +0x96
github.com/aws/eks-anywhere/pkg/task.(*taskRunner).RunTask(0xc00041a360, {0x3a65990, 0xc000126000}, 0xc0001320f0)
github.com/aws/eks-anywhere/pkg/task/task.go:155 +0x3e3
github.com/aws/eks-anywhere/pkg/workflows.(*Upgrade).Run(0xc000adfc80, {0x3a65990, 0xc000126000}, 0xc0002edd80, 0xc00041a330, 0xc00041a330, {0x3a32d80?, 0xc00056e640}, 0x0?)
github.com/aws/eks-anywhere/pkg/workflows/upgrade.go:78 +0x435
github.com/aws/eks-anywhere/cmd/eksctl-anywhere/cmd.(*upgradeClusterOptions).upgradeCluster(0x52758c0, 0x5253c00)
github.com/aws/eks-anywhere/cmd/eksctl-anywhere/cmd/upgradecluster.go:149 +0xa98
github.com/aws/eks-anywhere/cmd/eksctl-anywhere/cmd.glob..func26(0x5253c00?, {0x34ec5e9?, 0x3?, 0x3?})
github.com/aws/eks-anywhere/cmd/eksctl-anywhere/cmd/upgradecluster.go:37 +0x26
github.com/spf13/cobra.(*Command).execute(0x5253c00, {0xc00058c360, 0x3, 0x3})
github.com/spf13/cobra@v1.5.0/command.go:872 +0x694
github.com/spf13/cobra.(*Command).ExecuteC(0x5253200)
github.com/spf13/cobra@v1.5.0/command.go:990 +0x3b4
github.com/spf13/cobra.(*Command).Execute(...)
github.com/spf13/cobra@v1.5.0/command.go:918
github.com/spf13/cobra.(*Command).ExecuteContext(...)
github.com/spf13/cobra@v1.5.0/command.go:911
github.com/aws/eks-anywhere/cmd/eksctl-anywhere/cmd.Execute()
github.com/aws/eks-anywhere/cmd/eksctl-anywhere/cmd/root.go:59 +0x54
main.main()
github.com/aws/eks-anywhere/cmd/eksctl-anywhere/main.go:29 +0x125
```

**What you expected to happen**:

Upgrade of worker nodes to `2xlarge` instance.

**How to reproduce it (as minimally and precisely as possible)**:

Create an EKS-A Cluster on Snow with `large` instance of 3 node size for CP and DP and try to upgrade the instance type to `2xlarge` for workers alone.

**Anything else we need to know?**:

**Environment**:
- EKS Anywhere Release: v0.14.1
- EKS Distro Release:

Start at pkg/providers/snow/snow.go:197 in EnvMap, then follow the upgrade path through pkg/executables/clusterctl.go and pkg/workflows/upgrade.go shown in the stack trace. Reproduce the Snowball Edge worker instance-type upgrade and trace the nil value; done means upgrading from large to 2xlarge completes without the panic.

Written by the indexing model from the issue text.