Add Trace-Level Metrics to MetricGenerator

[keyolk]

It appears that the MetricGenerator currently supports only span-level metrics. It would be very useful if it could also generate trace-level metrics. Additionally, adding the ability to include custom labels on these metrics would significantly enhance its functionality.

Is there any ongoing work related to this? I couldn’t find any references or discussions on this feature.

[joe-elliott]

Some discussion here if you want to contribute: #3994