Only functions with recent metrics are discovered in sidebar

[arendjr]

The new Autometrics sidebar does function discovery by issuing an instant query for the function_calls_count metric and looking at the labels of the metrics coming back. Unfortunately, Prometheus only seems to return metrics for labels that have been recently used, so that functions that don't get used often/recently don't come back.

Related issue: prometheus/prometheus#11181

[emschwartz]

I think this is actually related to autometrics-dev/autometrics-rs#70. Metrics only appear when there is data unfortunately.

I opened this discussion to try to think how we might want to approach this situation in general: https://github.com/orgs/autometrics-dev/discussions/25