Adding a missing section about the `Allow users with up to Guest role to create groups and personal projects` option

What does this MR do?

A customer ran into a problem where they were unable to find the option on the user's profile to enable group creation. It turned out this was caused by disabling the Allow users with up to Guest role to create groups and personal projects admin setting.

This is described in Hide per-user group creation flag if global one is disabled and was introduced in Add control to limit guests and below to create project

@msedlakjakubowski please review this with the product team as I am not certain this is all correct

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