Split visibility settings into separates tables in API doc

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What does this MR do?

We had some customer questions about how exactly the *_access_level project settings (in the API) actually relate to the relevant features, it's not clear what disabled, private or enabled mean exactly. I got an engineer to check the code and they figured out these are the API settings for the Visibility, project features, permissions section of project settings, where:

• disabled: Disables the feature.
• private: Enables and sets the feature to Only project members.
• enabled: Enables and sets the feature to Everyone with access.

We should make this clearer in the doc. Instead of repeating these details in every single setting, I've split them out into their own tables, and mentioned the details just once at the top, and using the details column to link to the relevant features.

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