[Feature Request] Calculate a task completion rate based on its subtasks completion rate

[gsalvatella]

Is your feature request related to a problem? Please describe.

When a task has subtasks, its completion rate should be deferred to its subtasks completion rates. For instance, when all subtasks are completed, the task should also have a 100% completion rate.

Describe the solution you'd like

For tasks having subtasks (and only in this case), defer the completion rate calculation to the sum of its subtasks' completion rate. That is:

if task.subtasks:
    task.completion = sum([subtask.completion for subtask in task.subtasks])

Describe alternatives you've considered

No response

Additional context

No response