Metrics Explorer - Custom metrics, events and properties

This post introduces the ability to track custom metrics, events, and properties in Application Insights. It details how to use `TrackEvent()` with custom properties and metrics, and `TrackMetric()` for independent measurements. The post provides code examples for recording events like file uploads/downloads, including associated properties like file type and size, and metrics like load time. It also demonstrates tracking pure metrics such as processing queue length and CPU occupancy at regular intervals. The post clarifies when to use `TrackEvent()` versus `TrackMetric()` for different telemetry scenarios.