update CHANGELOG.md to include #6783

CHANGELOG.md

@@ -14,6 +14,7 @@ IMPROVEMENTS:
 * All Data Sources: adding validation for the `resource_group_name` field to not be empty where it's Required [GH-6864]
 * Data Source: `azurerm_virtual_machine` - export `identity` attribute [GH-6826]
 * `azurerm_api_management` - support for configuring the Developer Portal [GH-6724]
+* `azurerm_api_managment` - support for user assigned managed identities [GH-6783]
 * `azurerm_application_gateway` - support for WAF policies [GH-6105]
 * `azurerm_app_service_environment` - support specifying explicit resource group [GH-6821]
 * `azurerm_express_route_circuit` - de-provision and re-provision circuit when changing the bandwidth reduction [GH-6601]