set readonly property of contentStorageAccount to false (#11630)

Co-authored-by: Zhejun Zhao <[email protected]>

Author: zhejun97

specification/streamanalytics/resource-manager/Microsoft.StreamAnalytics/preview/2017-04-01-preview/streamingjobs.json

@@ -644,7 +644,7 @@
           "$ref": "#/definitions/JobStorageAccount"
         },
         "contentStoragePolicy": {
-          "readOnly": true,
+          "readOnly": false,
           "type": "string",
           "description": "Valid values are JobStorageAccount and SystemAccount. If set to JobStorageAccount, this requires the user to also specify jobStorageAccount property. .",
           "enum": [