GitLab

Updates Pace Plans to check for the status of delayed publishing
jobs on a continual basis to know when publishing is done for real.

closes LS-2759
flag = pace_plans

Test plan:
  - Enable Pace Plans feature flag and course settings
  - Make sure you have delayed_job running
  - Go to a course with a new or existing Pace Plan
  - Make some changes to the pace plan and click "Publish"
  - Expect to see the publishing status in the upper-right part of the
    screen show "Publishing plan..."
  - In the Dev Tools network tab, check to see that requests are being
    made to the /api/v1/progress/<id> every 3 seconds
  - Expect the status to change to "All changes published" once the
    delayed job has finished

  - Do something to introduce delay into the delayed job (set a
    breakpoint, add a sleep, etc...)
  - Make some more changes to the plan and click "Publish" again
  - Refresh the page to reload Pace Plans
  - Expect the publishing status to be "Publishing plan..." on initial
    load as well until the job completes

Extra credit:
  - Make the publish job error out by changing the publish code or
    something
  - Make some changes and publish again
  - Verify that the status changes from "Publishing plan..." to "All
    changes published" when the Progress API returns with a "failed"
    status (actually showing the error will be handled with another
    ticket)
  - Verify that the `pacePlans.publishingProgress` object in the Redux
    store's state contains a `failed` workflow_state and an errorm
    message

Change-Id: Iaf1db5b1c35627e15d8e1b6c534fc1e23b8e4409
Reviewed-on: https://gerrit.instructure.com/c/canvas-lms/+/276530

Tested-by: Service Cloud Jenkins <svc.cloudjenkins@instructure.com>
Reviewed-by: Ed Schiebel <eschiebel@instructure.com>
QA-Review: Ed Schiebel <eschiebel@instructure.com>
Product-Review: Peyton Craighill <pcraighill@instructure.com>