Add ability to quickly access output from a previous task in pipelines and workflows

[shhlife]

Is your feature request related to a problem? Please describe. When creating a pipeline you sometimes want to get the output from a task that's not the direct parent of the current task. Currently you can get to that by using: {{ structure.find_task('id').output.value }}, but it's not as clear and easy to use as {{ parent_output }}. It would be nice to have something that's easier to use, and as easy as it is with workflows: {{ parent_outputs['id'] }}

Describe the solution you'd like Because parent task output is grabbed like this:

• {{ parent_output }}
• {{ parent_outputs['id'] }}

It would be great if we could grab any task in a similar manner:

• {{ task_output['id'] }}

Describe alternatives you've considered

• {{ find_task['id'].output.value }} - but this isn't consistent with parent_output