Add UI feature to show whether OTLP data is being successfully exported

[tbrockman]

Use case

When having issues viewing your telemetry data in your backend, it's always a bit tricky to determine where the issue actually resides, for ex: is it the application that should be emitting data, is it collector configuration, any of the processing layers between?

We can help make that process easier for less experienced users by offering a visual indication that trace/log/metric export requests are successful.

Implementation

• Store a limited buffer of failed export requests (for traces/logs/metrics)
• When collector URLs are changed in the popup, emit sample telemetry
• For each collector URL input:
  • if the related buffer is empty (and we've emitted some telemetry), display a success symbol (circle with green check mark, likely)
  • If the buffer isn't empty, show an error symbol (which allows you to see some of the error details on click/hover?).
  • If it's indeterminate (no sample events sent since collector URL has changed), show a some sort of loading indicator.