az aks --enable-encryption-at-host failes

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**Describe the bug**
I am trying to create a kubernetes cluster following https://docs.microsoft.com/en-us/azure/aks/enable-host-encryption
and every time ( Both on my desktop, and in the cloud shell ) I get "The property 'securityProfile.encryptionAtHost' is not valid because the 'Microsoft.Compute/EncryptionAtHost' feature is not enabled for this subscription."

**To Reproduce**
Follow https://docs.microsoft.com/en-us/azure/aks/enable-host-encryption

```
az aks create --name Test4 -g UsWest2 -s Standard_DS2_v2 -l westus2 --enable-encryption-at-host
```

Which Gives
```
The behavior of this command has been altered by the following extension: aks-preview
Deployment failed. Correlation ID: 756cd0e1-2072-4dc9-9a41-68e78fc86f8c. VMSSAgentPoolReconciler retry failed: deployment operations failed with error messages: {
"code": "InvalidParameter",
"message": "The property 'securityProfile.encryptionAtHost' is not valid because the 'Microsoft.Compute/EncryptionAtHost' feature is not enabled for this subscription.",
"target": "securityProfile.encryptionAtHost"
}
```

**Expected behavior**
A Kubernetes Cluster is created with Host Encryption enabled

**Environment summary**
## Environment Summary
```
Linux-5.8.0-41-generic-x86_64-with-debian-bullseye-sid
Python 3.6.10
Installer: DEB

azure-cli 2.18.0

Extensions:
aks-preview 0.4.73
azure-devops 0.18.0

**Additional context**