Runbook properties provisioning states are incomplete

Migrating from [here](https://github.com/Azure/azure-sdk-for-net/issues/4399). Looks like all the provisioning states being returned by the service [here](https://github.com/Azure/azure-rest-api-specs/blob/master/specification/automation/resource-manager/Microsoft.Automation/stable/2015-10-31/definitions.json#L2787) are not defined in the Runbook properties.
The modelAsString needs to be set to true to avoid further breaking changes to the users and the enum list needs to be updated.
This needs to be fixed and the sdks regenerated.