Implement full vault backup and restore based on https://github.com/Azure/azure-rest-api-specs/blob/master/specification/keyvault/data-plane/Microsoft.KeyVault/preview/7.2/backuprestore.json. Note that restore should probably be implemented as an LRO, which would poll the "pending" endpoint instead of exposing it outright. I have Azure/azure-rest-api-specs#9806 opened to track.