Add "feature_page" key to categories where "marketing" is set to true

Why is this change being made?

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Adds a feature_page key which links to the appropriate section within the features page. This will be used to update the categories table with our platform page.

Currently there is a lack of uniformity when linking from the categories table to a feature. The idea is to keep users within about.gitlab.com and not direct them away. The CTA of the platform page is to get users to explore what GitLab has to offer and hopefully signup for a free trial.

This completes an item in gitlab-com/marketing/digital-experience/buyer-experience#3608 (closed)

Author and Reviewer Checklist

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