tracing in OTLP support configuring service_name

[fatsheep9146]

Is your proposal related to a problem?

For now, if we enable thanos tracing in OTLP and push the traces into jaeger, the traces will displayed with a default service name OTLPResourceNoServiceName, which is little bit confusing,

So I think we should support service_name option in OTLP config, in order to make the traces more clear in jaeger and any other systems to display traces.

Describe the solution you'd like

Support service_name option in OTLP config, in order to make the traces more clear in jaeger and any other systems to display traces.

[ahurtaud]

The PR is valid to me, however, if you want to do it before using the next version.
Setting OTEL_SERVICE_NAME environment variable works ;)