Create sensei pages on plugin activation without depending on onboarding completion

[Imran92]

Resolves #7187

Proposed Changes

Previously we created the sensei pages only when the user completed the onboarding. If for some reason the user didn't complete the onboarding or skipped it, the pages didn't get created, resulting in the users not finding the Courses page, they My Courses page etc. So now we are changing the logic to create the pages on Activation of the plugin. I haven't removed it from the onboarding though because if the pages are already there, it already skips creating them, so if a user somehow deletes those pages or wants to recreate these pages for some reason, we can just tell them to go through the onboarding URL.

Testing Instructions

1. Create a new site
2. Install a build of sensei from this branch
3. Skip the onboarding
4. Go to Pages
5. Check that the Sensei pages are created (Courses, My Courses, Course Completed etc)
6. Now install it on a new site again
7. This time complete the onboarding
8. Make sure it completes as expected

Pre-Merge Checklist

• PR title and description contain sufficient detail and accurately describe the changes
• Acceptance criteria is met
• Decisions are publicly documented
• Adheres to coding standards (PHP, JavaScript, CSS, HTML)
• All strings are translatable (without concatenation, handles plurals)
• Follows our naming conventions (P6rkRX-4oA-p2)
• Hooks (p6rkRX-1uS-p2) and functions are documented
• New UIs are responsive and use a mobile-first approach
• New UIs match the designs
• Different user privileges (admin, teacher, subscriber) are tested as appropriate
• Legacy courses (course without blocks) are tested
• Code is tested on the minimum supported PHP and WordPress versions
• User interface changes have been tested on the latest versions of Chrome, Firefox and Safari
• "Needs Documentation" label is added if this change requires updates to documentation
• Known issues are created as new GitHub issues

[codecov]

Codecov Report

Attention: 2 lines in your changes are missing coverage. Please review.

Comparison is base (e1885dd) 51.03% compared to head (06384bd) 51.04%.
Report is 11 commits behind head on trunk.

Additional details and impacted files

@@            Coverage Diff            @@
##              trunk    #7426   +/-   ##
=========================================
  Coverage     51.03%   51.04%           
- Complexity    11165    11167    +2     
=========================================
  Files           613      614    +1     
  Lines         47137    47148   +11     
  Branches        405      405           
=========================================
+ Hits          24058    24066    +8     
- Misses        22752    22755    +3     
  Partials        327      327           

Files	Coverage Δ
includes/admin/class-sensei-setup-wizard.php	43.65% <ø> (ø)
.../class-sensei-home-task-customize-course-theme.php	78.94% <100.00%> (+7.51%)	⬆️
includes/class-sensei-utils.php	52.70% <100.00%> (-0.09%)	⬇️
includes/clock/class-clock.php	100.00% <100.00%> (ø)
includes/class-sensei.php	24.39% <0.00%> (-0.11%)	⬇️

... and 5 files with indirect coverage changes

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[m1r0]

Thank you for implementing this! Works as described.