Update naming of duo group settings

What does this MR do and why?

As pointed out in the related issues, these settings are confusing, it's not clear what they apply to. The overall design is being revisited and a large refactor is on the way, but as a quick MVC to help users that are currently confused by this, let's just add GitLab Duo to the settings to make it clear which they apply to.

• Resolves Not clear why settings of disabled features are... (#462404 - closed)
• Related to Beta & Experiment group settings are confusing (#441381 - closed)
• Related to &13782

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