Restrict Content: Setup Wizard: Add option to specify form

[n7studios]

Summary

Support for gating content by subscribing to a Kit Form was added in this PR, but it wasn't included in the setup wizard.

This PR resolves by adding support for Kit Forms to the dropdown when using the setup wizard for gating content, and uses the same field description as used on the Post / Page meta box.

Testing

• testAddNewMemberContentDownloadsByForm: Test that the Add New Member Content > Downloads generates the expected Page and restricts content by the selected Form.
• testAddNewMemberContentCourseByForm: Test that the Add New Member Content > Course generates the expected Pages and restricts content by the selected Form.

Checklist

• I have written a test and included it in this PR
• I have run all tests and they pass
• The code passes when running the PHP CodeSniffer
• Code meets WordPress Coding Standards for PHP, HTML, CSS and JS
• Security and Sanitization requirements have been followed
• I have assigned a reviewer or two to review this PR (if you're not sure who to assign, we can do this step for you)

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[noelherrick]

I see you have a test for adding a form and restricting content based on that - where's the logic that actually checks that the subscriber has the form?

[n7studios]

I see you have a test for adding a form and restricting content based on that - where's the logic that actually checks that the subscriber has the form?

The test functions, as well as all of those in RestrictContentFormCest, call the testRestrictedContentByFormOnFrontend helper method, which performs these checks.