workflows: holdingpen details page improvements

* Adds 2 new stages for workflow objects error and waiting.

* Better display of workflow definition.

* Display of completed tasks.
1: D290 White spaces around docstring should be trimmed.
1: D400 First line should end with '.', not 'L'
23: D400 First line should end with '.', not 'g'
31: D400 First line should end with '.', not 'g'