Cumulative job duration (realtime) in the nextflow execution report

New feature

The nextflow execution report is a very helpful tool for profiling pipeline performance and resource allocation. The current report describes well the per-process distribution of runtimes, but does not report the cumulative realtime duration by process.

Use case

I have some process which run in reasonable amount of time, but are executed many thousands of times, leading to very large cumulative runtimes. These processes are great candidates for performance optimization, but do not stand out in the current report.

Suggested implementation

I currently derive this from the trace file, but it would be right at home as a cumulative runtime bar plot in a separate tab of the Job Duration section of the execution report.