General availability: Event source start options in Azure Time Series Insights Gen2

Azure Time Series Insights Gen2 has released a feature that enables you to specify how much pre-existing data, if any, your environment should ingest when configuring your [event source.](https://docs.microsoft.com/en-us/azure/time-series-insights/concepts-streaming-ingestion-event-sources) Previously, when you connected an Azure IoT Hub or Azure Event Hubs to an Azure Time Series Insights environment, the environment would ingest all of the data currently stored in the hub. Migrating an event source from one environment to another was complex and posed the risk of indexing duplicate data. When attaching an event source, you now have the following options: * EarliestAvailable: Ingest all pre-existing data stored within the IoT or Event Hub * EventSourceCreationTime: Begin ingesting data that arrives after the event source has been created. Any pre-existing data that was streamed prior to the creation of the event source will be ignored. This is the default setting in the Azure portal. * CustomEnqueuedTime: Your environment will ingest data from your custom enqueued time (UTC) forward. All events that were enqueued into your IoT or Event Hub at or after your custom enqueued time will be ingested and stored. All events that arrived prior to your custom enqueued time will be ignored. For more details and visual examples, view the [documentation](https://docs.microsoft.com/azure/time-series-insights/concepts-streaming-ingestion-event-sources#start-options). * Azure Time Series Insights * Features * [ Azure Time Series Insights](https://azure.microsoft.com/en-gb/products/time-series-insights/)