Github action workflow 'timeline' view.

**Is your feature request related to a problem? Please describe.**
Right now it is difficult to visualise how long a workflow ran for, especially if there is a workflow with lots of parallel / dependent steps. I know you can look at the durations etc, but a nicer visualisation is missing.

**Describe the solution you'd like**
When clicking on / viewing a completed workflow run, have some kind of horizontal 'timeline' view. You'd have horizontal bars indicating how long each job / step ran for.

**Additional context**
Add any other context or screenshots about the feature request here.

No files or tests are named. Start at the completed workflow run view and trace how job and step durations are currently exposed; done means a horizontal timeline clearly shows the duration and relative ordering of each job or step, including parallel and dependent work.

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