loadgen: OTel load generation tooling

In cmd/ directory, there are

• otelsoak
  • Load generator that is exactly an OTel collector. It sends load to an endpoint and never terminates.
  • Suitable for soak testing
• otelbench
  • Load generator based on OTel collector and Go benchmarking. It sends load to an endpoint, terminates after a configured duration, and outputs statistics.
  • Suitable for benchmarking

otelsoak and otelbench are synonymous to apmsoak and apmbench in elastic/apm-perf.