App Service SCMType should support `VSTSRM`

👋🏻

We've recently had a PR opened to add support for additional SCM Types in Terraform - internally this uses the Enum's generated from the SDK's (we're using API version `2018-02-01`, fwiw). As a part of this PR it turns out there's a value which is used by Azure Pipelines/VSTS which isn't documented in the Swagger: `VSTSRM` ([usage example](https://github.com/Microsoft/azure-pipelines-tasks/blob/master/Tasks/AzureRmWebAppDeploymentV4/operations/AzureAppServiceUtility.ts#L19))

Would it be possible to:

a) confirm that this value is supported by the API
b) expose this in the Swagger?

Thanks!

cc @hbuckle