GraphQL PMG - Add job action modal

What does this MR do and why?

Part 3 of 3 for #467279 (closed)

• Part 1 - Render job action buttons
• Part 2 - Job action mutations
• Part 3 - Confirmation modal < you are here

This MR wires in the job action modal. When you click an action button with a confirmation message, the necessary modal will appear. Clicking the confirm button should fire your mutation.

Screenshots or screen recordings

How to set up and validate locally

1. Navigate to a project (this example uses the flightjs group)
2. Navigate to the Pipeline Editor (Build > Pipeline editor)
3. Trigger a pipeline
4. Once the pipeline appears in the pipeline editor widget, click on a stage
5. You should see the dropdown with your manual job
6. Click play on the manual job to test out the modal.

Example gitlab-ci.yml of your manual job

another_job:
  script:
    - sleep 5
  when: manual
  manual_confirmation: Are you sure?