To-Do: Introduce "closed" state (BE)

Summary

This is the backend implementation issue for the issue to introduce a Todo "closed" state and a "Close all" button.

Proposal

• Todo has a new state called closed.
• On the Todos list page, there is a new button to "Close all" (to the left of the button to "Mark all as done").
• Clicking "Close all" has similar behavior to "Mark all as done". (If resolution_action has been introduced, the Todo resolution action value is close-all.)
• After clicking "Close all" it turns into "Undo close all" and has similar behavior to "Undo mark all as done".

Documentation

• Need to update doc/user/todos.md