Out of the box support for Gunicorn

[owais]

Setting up OpenTelemetry needs additional manual steps when working with gunicorn as documented here: https://opentelemetry-python.readthedocs.io/en/latest/examples/fork-process-model/README.html#gunicorn-post-fork-hook

This should not be required if a user is invokes the opentelemetry-instrument command to auto-instrument their gunicorn based service.

Hint: pre instrumentation hook might be helpful to implement this.

[adriangb]

Clarifying question: this is not a problem if users instrument from within a forked process right? They'd just get a lock within each process, which works fine.

[adamantike]

@adriangb, I think that's right. I'm currently using the approach detailed in #385 (comment), which instruments each process as expected.