Instrumentation: OpenTracing jaeger exporter vs. OpenTelemetry tracer feature parity

[yvrhdn]

This is an issue to track differences between the OpenTracing Jaeger exporter (the default) and the newer OpenTelemetry tracer. The OTel tracer was added to Tempo with #842 and is currently behind a feature flag (use_otel_tracer)
I'll update this issue has new problems show up and problems get solved.

The OpenTracing Jaeger client: https://github.com/jaegertracing/jaeger-client-go
The OpenTelemetry Jaeger exporter: https://github.com/open-telemetry/opentelemetry-go/tree/main/exporters/jaeger

Features missing

• Sampling can not be configured using environment variables
• No support for the Jaeger remote sampling protocol
  • PR to add this to otel-go: Add Jaeger remote sampler open-telemetry/opentelemetry-go-contrib#936
• In general, there are less environment variables to tune performance
  • For instance, we sometimes set JAEGER_REPORTER_MAX_QUEUE_SIZE but maybe this isn't necessary with otel-go?

[github-actions]

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