[exporter/azuremonitor] Refactor to use higher level api to send trace events

[whitneygriffith]

Description

1. Created the spanToTelemetry method to leverage the higher-level Track API, which is the recommended approach for sending traces to the queue. This refactor simplifies trace processing and aligns with best practices for handling telemetry data efficiently.
2. Resolved an issue where traces weren't being sent to App Insights due to not flushing the Telemetry Client. Added the necessary flush operation to ensure all traces are properly sent to the queue, leveraging App Insights' batch handling for more efficient processing.

Link to tracking issue

Part of #35037

I will follow up with updating the API used for sending metrics and logs as well. When this is done I will deprecate the transportChannel which uses the lower level Send() method