[ReleasePR containerinstance] S360 Fixes: Dev containerinstance microsoft.container instance 2021 09 01 (#2540)

Create to sync Azure/azure-rest-api-specs#20199
[ReCreate this PR](https://github.com/azure-resource-manager-schemas/compare/main...azure-sdk:sdkAuto/containerinstance?expand=1)

Author: msftbot[bot]

schemas/2021-09-01/Microsoft.ContainerInstance.json

@@ -35,7 +35,7 @@
         "properties": {
           "oneOf": [
             {
-              "$ref": "#/definitions/ContainerGroupProperties"
+              "$ref": "#/definitions/ContainerGroupPropertiesProperties"
             },
             {
               "$ref": "https://schema.management.azure.com/schemas/common/definitions.json#/definitions/expression"
@@ -122,10 +122,6 @@
       ],
       "description": "The properties of the Azure File volume. Azure File shares are mounted as volumes."
     },
-    "Components10wh5udschemascontainergroupidentitypropertiesuserassignedidentitiesadditionalproperties": {
-      "type": "object",
-      "properties": {}
-    },
     "Container": {
       "type": "object",
       "properties": {
@@ -213,20 +209,20 @@
             {
               "type": "object",
               "additionalProperties": {
-                "$ref": "#/definitions/Components10wh5udschemascontainergroupidentitypropertiesuserassignedidentitiesadditionalproperties"
+                "$ref": "#/definitions/UserAssignedIdentities"
               },
               "properties": {}
             },
             {
               "$ref": "https://schema.management.azure.com/schemas/common/definitions.json#/definitions/expression"
             }
           ],
-          "description": "The list of user identities associated with the container group. The user identity dictionary key references will be ARM resource ids in the form: '/subscriptions/{subscriptionId}/resourceGroups/{resourceGroupName}/providers/Microsoft.ManagedIdentity/userAssignedIdentities/{identityName}'."
+          "description": "The list of user identities associated with the container group."
         }
       },
       "description": "Identity for the container group."
     },
-    "ContainerGroupProperties": {
+    "ContainerGroupPropertiesProperties": {
       "type": "object",
       "properties": {
         "containers": {
@@ -859,8 +855,7 @@
         }
       },
       "required": [
-        "server",
-        "username"
+        "server"
       ],
       "description": "Image registry credential."
     },
@@ -1188,6 +1183,11 @@
       ],
       "description": "The resource requirements."
     },
+    "UserAssignedIdentities": {
+      "type": "object",
+      "properties": {},
+      "description": "The list of user identities associated with the container group. The user identity dictionary key references will be ARM resource ids in the form: '/subscriptions/{subscriptionId}/resourceGroups/{resourceGroupName}/providers/Microsoft.ManagedIdentity/userAssignedIdentities/{identityName}'."
+    },
     "Volume": {
       "type": "object",
       "properties": {