System topics are now an Azure resource

Explicitly create system topics using Azure Event Grid. Previously, a system topic was implicit and wasn't exposed for simplicity. With this new update, system topics are visible as an Azure resource and these additional capabilities are now available: * Manage system topics * Manage event subscriptions for system topics * Set up diagnostic logs for system topics * Set up alerts on publish and delivery metrics [Learn more](https://docs.microsoft.com/en-us/azure/event-grid/system-topics). * Event Grid * Features * [ Event Grid](https://azure.microsoft.com/en-gb/products/event-grid/)