Using the exporter without the locust WebUI

Is this possible at all?
I have an automated build that spins up a container and runs locust with the `headless` flag so I can set the run-time.
This means the stats/requests endpoint is not available and the exporter can't read it.

I found a way to get around this by using locust as an API:
example from https://github.com/locustio/locust/blob/master/examples/use_as_lib.py
```
# setup Environment and Runner
env = Environment(user_classes=[User])
env.create_local_runner()

# start a WebUI instance
env.create_web_ui("127.0.0.1", 8089)

# start a greenlet that periodically outputs the current stats
gevent.spawn(stats_printer(env.stats))

# start the test
env.runner.start(1, hatch_rate=10)

# in 60 seconds stop the runner
gevent.spawn_later(60, lambda: env.runner.quit())

# wait for the greenlets
env.runner.greenlet.join()

# stop the web server for good measures
env.web_ui.stop()
```

Is there a better way to do this?

Start by checking how the exporter reads Locust's stats/requests endpoint in the headless flow described. Read Locust's examples/use_as_lib.py to understand the suggested API-based setup. Done means the exporter can obtain metrics when Locust runs without its WebUI, with the behavior covered by appropriate tests.

Written by the indexing model from the issue text.