Create required pages on activation

[brianhogg]

NOTE: Verify we also want to create the Course and Membership catalog pages, as this may stop the taxonomy page from working if that's what the user setup

Description

Create the four required pages on activation or update, if they don't already exist.

Fixes #2638

How has this been tested?

Manually

Checklist:

• [ ] This PR requires and contains at least one changelog file. <!-- To create a changelog yml file: npm run dev changelog add -- -i and follow the prompt. See also: https://github.com/gocodebox/lifterlms/blob/trunk/packages/dev/README.md#changelog-add -->
• [ ] My code has been tested.
• [ ] My code passes all existing automated tests.
• [ ] My code follows the LifterLMS Coding & Documentation Standards.

[brianhogg]

Potential complication is the checkbox for streamlined approach with PMPro would never display. Could see if PMPro can assume they want the streamlined approach on first install?

We could not try to create or modify the course or membership pages of create_pages has happened already.

[ideadude]

FYI here is the code PMPro uses to "streamline" the setup. https://github.com/strangerstudios/paid-memberships-pro/blob/dev/includes/compatibility/lifterlms.php#L397-L435

[ideadude]

This requires a larger "pitch" before we alter the wizard in this way.