Metric showing in progress tasks and celery_task_total inconsistency

[Lameorc]

Hi,

The readme seems to suggest that the celery_tasks_total is a gauge but it's implemented as a Counter.

Is there any plan to "revert" this to a gauge showing the inflight tasks in each state currently? Or even introduce a new metric that covers this use case.

Thanks

[SharpEdgeMarshall]

celery_total_task should be reported as Counter in documentation.

We could consider a gauge version for actual queue length like asked in #25