Add "Publish your first course" task

[fjorgemota]

trafficstars

Fixes #5639

Changes proposed in this Pull Request

• Add Publish your First Course task;
• Add tests for the task added;
• Register task on the provider;

Testing instructions

On a WP installation containing Sensei LMS on this branch:

1. Run curl --user "user:application password" http://your-host/wp-json/sensei-internal/v1/home and make sure that the task "Publish your first Course" has done set to false, with the URL pointing to create a new course;
2. Create a course/import the sample course, and verify if that task still has done set to false, with the URL still pointing to create a new course.
3. Publish the sample course, and verify if that task still has done set to false, with the URL still pointing to create a new course;
4. Now, create another course, and verify if that task still has done set to false, but with the URL now pointing to the edit page for that course you just created;
5. Publish the course you just created, and verify if that task now has done set to true, and the URL is now null;

[codecov[bot]]

Codecov Report

Merging #5888 (9e2f753) into remove/image-tasks-sensei-home (dd52b8b) will increase coverage by 0.03%. The diff coverage is 73.33%.

@@                         Coverage Diff                          @@
##             remove/image-tasks-sensei-home    #5888      +/-   ##
====================================================================
+ Coverage                             43.84%   43.87%   +0.03%     
- Complexity                             9137     9149      +12     
====================================================================
  Files                                   439      440       +1     
  Lines                                 32514    32544      +30     
  Branches                                252      252              
====================================================================
+ Hits                                  14255    14278      +23     
- Misses                                18073    18080       +7     
  Partials                                186      186              

Impacted Files	Coverage Δ
...sk/class-sensei-home-task-publish-first-course.php	72.41% <72.41%> (ø)
...in/home/tasks/class-sensei-home-tasks-provider.php	100.00% <100.00%> (ø)
includes/class-sensei-quiz.php	59.34% <0.00%> (+0.13%)	:arrow_up:

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[fjorgemota]

I just rebased this branch over the changes on the feature/new-onboarding-wizard, and I fixed the conflict in that merge. I decided to rebase instead of merge because I assume no one downloaded this branch yet for review.

If you did, just delete your local branch and redownload again, please. :)