[ReleasePR eventgrid] Adding missing identity properties and ExtensionTopics operation (#1968)

Create to sync Azure/azure-rest-api-specs#16469
[ReCreate this PR](https://github.com/azure-resource-manager-schemas/compare/main...AzureSDKAutomation:sdkAuto/eventgrid?expand=1)

Author: msftbot[bot]

schemas/2021-12-01/Microsoft.EventGrid.json

@@ -281,6 +281,17 @@
             "2021-12-01"
           ]
         },
+        "identity": {
+          "oneOf": [
+            {
+              "$ref": "#/definitions/IdentityInfo"
+            },
+            {
+              "$ref": "https://schema.management.azure.com/schemas/common/definitions.json#/definitions/expression"
+            }
+          ],
+          "description": "The identity information for the resource."
+        },
         "location": {
           "type": "string",
           "description": "Location of the resource."
@@ -612,6 +623,34 @@
       "properties": {},
       "description": "Information about the dead letter destination for an event subscription. To configure a deadletter destination, do not directly instantiate an object of this class. Instead, instantiate an object of a derived class. Currently, StorageBlobDeadLetterDestination is the only class that derives from this class."
     },
+    "DeadLetterWithResourceIdentity": {
+      "type": "object",
+      "properties": {
+        "deadLetterDestination": {
+          "oneOf": [
+            {
+              "$ref": "#/definitions/DeadLetterDestination"
+            },
+            {
+              "$ref": "https://schema.management.azure.com/schemas/common/definitions.json#/definitions/expression"
+            }
+          ],
+          "description": "Information about the dead letter destination for an event subscription. To configure a deadletter destination, do not directly instantiate an object of this class. Instead, instantiate an object of a derived class. Currently, StorageBlobDeadLetterDestination is the only class that derives from this class."
+        },
+        "identity": {
+          "oneOf": [
+            {
+              "$ref": "#/definitions/EventSubscriptionIdentity"
+            },
+            {
+              "$ref": "https://schema.management.azure.com/schemas/common/definitions.json#/definitions/expression"
+            }
+          ],
+          "description": "The identity information with the event subscription."
+        }
+      },
+      "description": "Information about the deadletter destination with resource identity."
+    },
     "DeliveryAttributeMapping": {
       "type": "object",
       "oneOf": [
@@ -630,6 +669,34 @@
       },
       "description": "Delivery attribute mapping details."
     },
+    "DeliveryWithResourceIdentity": {
+      "type": "object",
+      "properties": {
+        "destination": {
+          "oneOf": [
+            {
+              "$ref": "#/definitions/EventSubscriptionDestination"
+            },
+            {
+              "$ref": "https://schema.management.azure.com/schemas/common/definitions.json#/definitions/expression"
+            }
+          ],
+          "description": "Information about the destination for an event subscription."
+        },
+        "identity": {
+          "oneOf": [
+            {
+              "$ref": "#/definitions/EventSubscriptionIdentity"
+            },
+            {
+              "$ref": "https://schema.management.azure.com/schemas/common/definitions.json#/definitions/expression"
+            }
+          ],
+          "description": "The identity information with the event subscription."
+        }
+      },
+      "description": "Information about the delivery for an event subscription with resource identity."
+    },
     "DomainProperties": {
       "type": "object",
       "properties": {
@@ -973,6 +1040,31 @@
       },
       "description": "Filter for the Event Subscription."
     },
+    "EventSubscriptionIdentity": {
+      "type": "object",
+      "properties": {
+        "type": {
+          "oneOf": [
+            {
+              "type": "string",
+              "enum": [
+                "SystemAssigned",
+                "UserAssigned"
+              ]
+            },
+            {
+              "$ref": "https://schema.management.azure.com/schemas/common/definitions.json#/definitions/expression"
+            }
+          ],
+          "description": "The type of managed identity used. The type 'SystemAssigned, UserAssigned' includes both an implicitly created identity and a set of user-assigned identities. The type 'None' will remove any identity."
+        },
+        "userAssignedIdentity": {
+          "type": "string",
+          "description": "The user identity associated with the resource."
+        }
+      },
+      "description": "The identity information with the event subscription."
+    },
     "EventSubscriptionProperties": {
       "type": "object",
       "properties": {
@@ -987,6 +1079,28 @@
           ],
           "description": "Information about the dead letter destination for an event subscription. To configure a deadletter destination, do not directly instantiate an object of this class. Instead, instantiate an object of a derived class. Currently, StorageBlobDeadLetterDestination is the only class that derives from this class."
         },
+        "deadLetterWithResourceIdentity": {
+          "oneOf": [
+            {
+              "$ref": "#/definitions/DeadLetterWithResourceIdentity"
+            },
+            {
+              "$ref": "https://schema.management.azure.com/schemas/common/definitions.json#/definitions/expression"
+            }
+          ],
+          "description": "Information about the deadletter destination with resource identity."
+        },
+        "deliveryWithResourceIdentity": {
+          "oneOf": [
+            {
+              "$ref": "#/definitions/DeliveryWithResourceIdentity"
+            },
+            {
+              "$ref": "https://schema.management.azure.com/schemas/common/definitions.json#/definitions/expression"
+            }
+          ],
+          "description": "Information about the delivery for an event subscription with resource identity."
+        },
         "destination": {
           "oneOf": [
             {