Report the elapsed time for each workflow step (#2700)

* Report the elapsed time for each workflow step

The `runStepExecutor` was extended to track and report the execution time of the step.

This applies both to the standard and JSON log format.

Please, note that:
- on the standard log the time format depends on the value (e.g. `3.038334954s` or `2m0.054014069s`)
- on the JSON log the time format is nanoseconds

* Added the `executionTime` report also to failing steps