IoT Hub Device Provisioning Service missing specs

There is no REST API spec for Version 2019-03-31. It would be great if this was available so that the Device Provisioning Service Enrollment Group APIs could be exposed to the Go SDK (ref [azure-sdk-for-go](https://github.com/Azure/azure-sdk-for-go/))

Example API to use: [Create or Update Enrollment Group](https://docs.microsoft.com/en-us/rest/api/iot-dps/createorupdateenrollmentgroup/createorupdateenrollmentgroup)

Start with the linked Create or Update Enrollment Group REST API documentation and compare it with the existing IoT Hub Device Provisioning Service specifications. Add the missing REST API specification for version 2019-03-31 so the Device Provisioning Service Enrollment Group APIs can be exposed to the Go SDK.

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