pixl populate updates rate if its zero

[stefpiatek]

Definition of Done / Acceptance Criteria

As a pixl pipeline runner, I want the pixl populate command to only update the rate of processing from a queue if the current rate is 0, if its been set to something else then I don't want to change it

Testing

fine to this to be a mocked response from the api call to get query rate, test for 0 and test for a positive number seems reasonable.

Documentation

Update documentation for CLI argument

Dependencies

No response

Details and Comments

No response