Missing Swagger for Stream Analytics API `2017-04-01-preview`

:wave:

At this time [the Stream Analytics Swagger](https://github.com/Azure/azure-rest-api-specs/tree/master/specification/streamanalytics/resource-manager) only has support for API Version `2016-03-01` - however to make use of a `compatibilityLevel` of `1.2` API version `2017-04-01-preview` must be used.

Attempting to provision `compatibilityLevel` of `1.2` using the older API with the following HTTP Request:

```
:authority: management.azure.com
:method: PUT
:path: /subscriptions/00000000-0000-0000-0000-000000000000/resourcegroups/tom-devstreama/providers/Microsoft.StreamAnalytics/streamingjobs/tomdev-sa99?api-version=2016-03-01
:scheme: https
content-type: application/json; charset=utf-8
user-agent: Go/go1.11.5 (amd64-darwin) go-autorest/v11.7.0 Azure-SDK-For-Go/v26.7.0 streamanalytics/2016-03-01 Terraform/0.11.14 terraform-provider-azurerm/dev
authorization: Bearer XXXXXXXXXX
content-length: 432
accept-encoding: gzip

{
"location": "westeurope",
"name": "tomdev-sa99",
"properties": {
"sku": {
"name": "Standard"
},
"eventsOutOfOrderPolicy": "Adjust",
"outputErrorPolicy": "Drop",
"eventsOutOfOrderMaxDelayInSeconds": 50,
"eventsLateArrivalMaxDelayInSeconds": 60,
"dataLocale": "en-GB",
"compatibilityLevel": "1.2",
"transformation": {
"name": "Transformation",
"properties": {
"streamingUnits": 3,
"query": " SELECT *\n INTO [YourOutputAlias]\n FROM [YourInputAlias]\n"
}
}
}
}
```

returns the response:

```
cache-control: no-store, no-cache
pragma: no-cache
content-length: 447
content-type: application/json; charset=utf-8
expires: -1
x-aspnetmvc-version: 5.0
x-ms-request-id: 96015f4c-87a3-4ee8-9926-be994b702481
x-ms-ratelimit-remaining-subscription-writes: 1199
server: Microsoft-IIS/8.5
x-powered-by: ASP.NET
x-ms-correlation-request-id: 61a3efb9-631c-4f48-89d8-8a15aa3808d2
x-ms-routing-request-id: UKSOUTH:20190410T094111Z:61a3efb9-631c-4f48-89d8-8a15aa3808d2
strict-transport-security: max-age=31536000; includeSubDomains
x-content-type-options: nosniff
date: Wed, 10 Apr 2019 09:41:11 GMT

{
"code": "422",
"message": "Feature compatibilityLevel with value 1.2 is not supported in API version 2016-03-01.1.10. Please use API version 2017-04-01-preview.1.12.",
"details": {
"code": "422",
"message": "Feature compatibilityLevel with value 1.2 is not supported in API version 2016-03-01.1.10. Please use API version 2017-04-01-preview.1.12.",
"correlationId": "61a3efb9-631c-4f48-89d8-8a15aa3808d2",
"requestId": "96015f4c-87a3-4ee8-9926-be994b702481"
}
}
```

So that we can fully support this feature, would it be possible to add the Swagger for the new API version?

Thanks!

Start in specification/streamanalytics/resource-manager and inspect the existing 2016-03-01 Swagger definition. Add the missing 2017-04-01-preview API specification, preserving the existing Stream Analytics resource structure. Done means the preview version is represented in the REST specifications and supports compatibilityLevel 1.2.

Written by the indexing model from the issue text.