Refines #8 to get duration for the pipeline
Issue #8 (closed) wasn't completely fulfilled by the related MR, but close enough, now this issue would be specifically to calculate the duration of a pipeline with a breakdown per job.
The duration of the pipeline could be done by supplying the ID, then getting the started_at and finished_at properties, but then it would also be good to have a breakdown about which jobs took the longest. For that we will need to query the jobs for the pipeline and try to get the duration for those.