Update feature category to ai_abstraction_layer

What does this MR do and why?

Since Settings > GitLab Duo menu item belongs to groupai framework, and was originally implemented by them, and seems to be unrelated to Duo Chat in specific.

MR acceptance checklist

Please evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.

Screenshots or screen recordings

N/A

How to set up and validate locally

N/A

Related to #482501