Add to do widget for work items

What does this MR do and why?

The widget will add a work item to to-do list or can be resolved from the list.

Screenshots or screen recordings

Screen_Recording_2023-04-25_at_4.33.15_PM

How to set up and validate locally

Prerequisites: Enable the following feature flags to create objects supporting this feature using gdk rails console:

1. Feature.enable(:work_items_mvc)
2. Feature.enable(:okrs_mvc, Project.find_by_full_path('gitlab-org/gitlab-test'))

Steps:

1. Go to any Project > Issues > List
2. Create an new Objective
3. Go to Objective detail page
4. Click on the checkbox button
5. Clicking on it again will mark it as done

On similar lines, a key result can be added to the objective in the Child objectives and key results section. And a task comes under an issue Tasks section.

In both, there is an option to add task/key result.

Steps to check with modal:

1. Go to any Project > Issues > List
2. Create an Objective or Issue
3. Go to Objective/Issue detail page > Child objectives and key results/Tasks section
4. Add a Key result/Task
5. Click on the newly added item
6. Click on the checkbox button
7. Clicking on it again will mark it as done

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

Related to #390549 (closed)