feat: prombench to measure OTLP endpoint performace

[krajorama]

Idea

Authors: @jesusvazquez @krajorama

Implement measuring OTLP endpoint performance and showing on dashboard.

This only concerns ingestion of data as OTLP has no read path for metrics at the moment.

Implementation idea 1

Since OTLP is a first class citizen, this should not be optional.

Start another Prometheus instance and send it OTLP traffic and measure.

Implementation idea 2

Make it an option of prombench whether to run scrape based test or OTLP ingestion based test (or combine?).

[ArthurSens]

This tool might be useful :)

https://github.com/open-telemetry/opentelemetry-collector-contrib/tree/main/cmd/telemetrygen