[DataFactory]Add support for running staging on multiple sources in parallel (Azure#18956)

* Add support for running staging on multiple sources in parallel

* update

Author: kesharma

specification/datafactory/resource-manager/Microsoft.DataFactory/stable/2018-06-01/entityTypes/Pipeline.json

@@ -7421,6 +7421,10 @@
         "runConcurrently": {
           "description": "Concurrent run setting used for data flow execution. Allows sinks with the same save order to be processed concurrently. Type: boolean (or Expression with resultType boolean)",
           "type": "object"
+        },
+        "sourceStagingConcurrency": {
+          "description": "Specify number of parallel staging for sources applicable to the sink. Type: integer (or Expression with resultType integer)",
+          "type": "object"
         }
       },
       "required": [