Dev batch microsoft.batch 2019 04 01- Fix swagger spec incorrect null…

…able property (#5720)

* Adds base for updating Microsoft.Batch from version stable/2018-12-01 to version 2019-04-01

* Updates readme

* Updates API version in new specs and examples

* add per family quota changes

* update the pfq values and descriptions

* Update specification/batch/resource-manager/Microsoft.Batch/stable/2019-04-01/BatchManagement.json

Co-Authored-By: jafreck <jafreck@microsoft.com>

* update quota fields with usersubscription behavior

* update descriptions from null to not returned

* remove duplicate text

* correct nullable properties

specification/batch/resource-manager/Microsoft.Batch/stable/2019-04-01/BatchManagement.json

@@ -2013,15 +2013,15 @@
         },
         "dedicatedCoreQuota": {
           "readOnly": true,
-          "x-nullable": false,
+          "x-nullable": true,
           "type": "integer",
           "format": "int32",
           "title": "The dedicated core quota for the Batch account.",
           "description": "For accounts with PoolAllocationMode set to UserSubscription, quota is managed on the subscription so this value is not returned."
         },
         "lowPriorityCoreQuota": {
           "readOnly": true,
-          "x-not-returnable": false,
+          "x-nullable": true,
           "type": "integer",
           "format": "int32",
           "title": "The low-priority core quota for the Batch account.",