CodeGen from PR 18349 in Azure/azure-rest-api-specs

Event Grid: add support for 2021-10-15-preview API version (#18349)

* Using 2021-06-01-preview files as a baseline

* Add swagger, example, and readme files for 2021-10-15-preview API version

* Fix prettier errors and missing files

* Fix Python readme file

* Remove references to common-types files

* Fix missing brace in example file

* Fix ModelValidation errors

* Fix more ModelValidation errors

* Fix more ModelValidation errors

* Make systemData read only

* Run prettier for Channels_Update.json

* Fix various linter errors

* Data residency boundary fix

Author: SDKAuto

schemas/2018-05-01/subscriptionDeploymentTemplate.json

@@ -884,6 +884,9 @@
             {
               "$ref": "https://schema.management.azure.com/schemas/2021-06-01-preview/Microsoft.EventGrid.json#/unknown_resourceDefinitions/eventSubscriptions"
             },
+            {
+              "$ref": "https://schema.management.azure.com/schemas/2021-10-15-preview/Microsoft.EventGrid.json#/unknown_resourceDefinitions/eventSubscriptions"
+            },
             {
               "$ref": "https://schema.management.azure.com/schemas/2021-12-01/Microsoft.EventGrid.json#/unknown_resourceDefinitions/eventSubscriptions"
             },