The identity type in `containerregistry` is returned with the first letter in lower case

Problematic swagger: https://github.com/Azure/azure-rest-api-specs/blob/d1d7dc3a6885ab3d68fcdfbea101d1e4f6284458/specification/containerregistry/resource-manager/Microsoft.ContainerRegistry/preview/2019-12-01-preview/containerregistry.json#L1835

Request URL:
```
PUT /subscriptions/REDACTED/resourceGroups/dapzhang-acr/providers/Microsoft.ContainerRegistry/registries/acr48827?api-version=2019-12-01-preview HTTP/1.1
```
Request body:
```
{
"identity": { "type": "SystemAssigned" },
"location": "westus2",
"properties": { "adminUserEnabled": false },
"sku": { "name": "Premium", "tier": "Premium" },
"tags": {}
}
```
Response of a GET request after the creation:
```
{
"sku": { "name": "Premium", "tier": "Premium" },
"type": "Microsoft.ContainerRegistry/registries",
"identity": {
"principalId": "REDACTED",
"tenantId": "REDACTED",
"type": "systemAssigned"
},
"id": "/subscriptions/REDACTED/resourceGroups/dapzhang-acr/providers/Microsoft.ContainerRegistry/registries/acr48827",
"name": "acr48827",
"location": "westus2",
"tags": {},
"properties": {
"loginServer": "acr48827.azurecr.io",
"creationDate": "2020-08-06T08:03:30.0241751Z",
"provisioningState": "Succeeded",
"adminUserEnabled": false,
"networkRuleSet": {
"defaultAction": "Allow",
"virtualNetworkRules": [],
"ipRules": []
},
"policies": {
"quarantinePolicy": { "status": "disabled" },
"trustPolicy": { "type": "Notary", "status": "disabled" },
"retentionPolicy": {
"days": 7,
"lastUpdatedTime": "2020-08-06T08:03:31.2308023+00:00",
"status": "disabled"
}
},
"encryption": { "status": "disabled" },
"dataEndpointEnabled": false,
"dataEndpointHostNames": [],
"privateEndpointConnections": [],
"publicNetworkAccess": "Enabled"
}
}
```

As you can see, in the GET response, the `type` of `identity` is `systemAssigned` instead of `SystemAssigned`