[load-generator] Replace locust with a lightweight load testing tool

[rogercoll]

The opentelemetry-demo deployment requires about ~5/6 GiB of free memory, being the load-generator the highest memory consumption service.

Related issues:

• [load-generator] High Memory Consumption #2678

Possible alternative to research: https://github.com/grafana/crocochrome + https://github.com/grafana/k6

[rohanarora]

Roger (@rogercoll), Our experience has been that the memory attribution largely comes from when the browser traffic via Locust is enabled is what our experience has been. It is the default setting which results in Chromium-based processes.

So toggling the environment variable/configuration LOCUST_BROWSER_TRAFFIC_ENABLED to false results in the relatively light-weight (less memory intensive) load test.