Document read-only system id property for Power Platform account and enterprise policy resources (#19617)

Author: dkappes-msft

specification/powerplatform/resource-manager/Microsoft.PowerPlatform/preview/2020-10-30-preview/account.json

@@ -397,6 +397,11 @@
       "type": "object",
       "description": "The properties that define configuration for the account.",
       "properties": {
+        "systemId": {
+          "type": "string",
+          "description": "The internally assigned unique identifier of the resource.",
+          "readOnly": true
+        },
         "description": {
           "type": "string",
           "description": "The description of the account."

specification/powerplatform/resource-manager/Microsoft.PowerPlatform/preview/2020-10-30-preview/enterprisePolicy.json

@@ -458,6 +458,11 @@
       "type": "object",
       "description": "The properties that define configuration for the enterprise policy.",
       "properties": {
+        "systemId": {
+          "type": "string",
+          "description": "The internally assigned unique identifier of the resource.",
+          "readOnly": true
+        },
         "lockbox": {
           "type": "object",
           "description": "Settings concerning lockbox.",