[FEATURE] Make step details available for use by later steps

**Is your feature request related to a problem? Please describe.**
I want to be able to log the start & end times and duration of each step. A time and duration are available on the Details tab of most, maybe all, steps, but they are not available as part of steps..context or steps..exports, etc.

**Describe the solution you'd like**
There should be a steps..exports.metrics or steps..context.metrics, or even just steps..metrics (which Pi suggests as an available option today). It should contain, at minimum, start_time and duration_ms. It could also contain end_time, though that's computable from the other two, provided that start_time is to the millisecond. It should also contain any other metrics deemed relevant based on the type of step in play.

**Do you have a workaround?**
No

**Comparable features in other tools?**
Not sure this is relevant

**Additional context**
None.