ApplicationInsights Workbook: etag is described as a dictionary instead of a string

The `etag` of the workbook's `Resource` is described as a dictionary of strings (same as `tags`):

https://github.com/Azure/azure-rest-api-specs/blob/752ca4a79d1e587d95567a62d98b63f55bd6fced/specification/applicationinsights/resource-manager/Microsoft.Insights/stable/2021-03-08/workbooks_API.json#L464-L467

While the actual API returns a plain string:

```json
{
"id": "/subscriptions/sub/resourcegroups/myresourcegroup6c9be5a1/providers/microsoft.insights/workbooks/id",
"name": "id",
"type": "microsoft.insights/workbooks",
"location": "westeurope",
"tags": {
"hidden-title": "My workbook"
},
"kind": "shared",
"etag": "\"8500d7d1-0000-0200-0000-60cb5c2f0000\""
}
```

Please change `etag` to

```
"etag": {
"type": "string",
"description": "Resource etag"
}
```

Open specification/applicationinsights/resource-manager/Microsoft.Insights/stable/2021-03-08/workbooks_API.json at the Resource schema around lines 464-467 and compare etag with the example response in the issue. Update the etag schema to describe a string while leaving tags as a dictionary; done when the specification matches the API response.

Written by the indexing model from the issue text.