Change type of Ssis actitvity's packagePath, runtime, loggingLevel and (

Azure#4939)

environmentPath from string to object, so that we can use expression for
these properties

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

@@ -2094,24 +2094,16 @@
           "$ref": "#/definitions/SSISPackageLocation"
         },
         "runtime": {
-          "description": "Specifies the runtime to execute SSIS package.",
-          "type": "string",
-          "enum": [
-            "x64",
-            "x86"
-          ],
-          "x-ms-enum": {
-            "name": "SSISExecutionRuntime",
-            "modelAsString": true
-          }
+          "description": "Specifies the runtime to execute SSIS package. The value should be \"x86\" or \"x64\". Type: string (or Expression with resultType string).",
+          "type": "object"
         },
         "loggingLevel": {
-          "description": "The logging level of SSIS package execution.",
-          "type": "string"
+          "description": "The logging level of SSIS package execution. Type: string (or Expression with resultType string).",
+          "type": "object"
         },
         "environmentPath": {
-          "description": "The environment path to execute the SSIS package.",
-          "type": "string"
+          "description": "The environment path to execute the SSIS package. Type: string (or Expression with resultType string).",
+          "type": "object"
         },
         "connectVia": {
           "description": "The integration runtime reference.",
@@ -2163,8 +2155,8 @@
       "type" : "object",
       "properties": {
         "packagePath": {
-          "description": "The SSIS package path.",
-          "type": "string"
+          "description": "The SSIS package path. Type: string (or Expression with resultType string).",
+          "type": "object"
         }
       },
       "required": [