[Docs] Update Duo Agentic Chat Labels and Naming for 18.2 – From Experiment to Beta

Goal

Ensure that all Duo Agentic Chat-related labels, prompts, titles, and user-facing references in the GitLab monolith reflect the Beta release status, removing or updating any remaining references to the experimental phase.

Open Questions

1. Are the changes already merged or prepared to be merged?, If yes, please link the relevant MR(s) below.
2. Is the release process for this system automatic or manual? If manual, what additional steps are required?
3. What is the estimated time it takes from merge to being live in front of users?
4. What is the latest safe merge deadline to ensure the changes are visible to users by July 17?