Include service name label in span receiver/exporter metrics

[linjmeyer]

Is your feature request related to a problem? Please describe. When collecting traces/spans there are several metrics created (e.g. exporter_send_failed_spans). These metrics do not include the span's service name. Other collectors (e.g. Jaeger Collector) add this label, which is very helpful when determining which services are sending the most spans/traces.

Describe the solution you'd like It would be helpful to include labels with the service name (e.g. exporter_send_failed_spans{svc="my-service"}) to identify if a particular service is sending a high amount of spans.

Describe alternatives you've considered If using an indexed storage backend you can query it directly (e.g. Elastic/Kibana) to get this info. This is not possible when using un-indexed storages like Grafana Tempo.

Additional context This was originally a feature request for grafana/agent which uses this repo.

[andrewhsu]

from the triage mtg today, setting to p3 allowed for if this change does not affect perf