Update Data Analyst Agent documentation to GA status
### Problem to solve
The Data Analyst Agent user documentation currently reflects Beta status and needs to be updated to GA status before the general availability release.
### Proposal
Update the [Data Analyst Agent documentation](https://docs.gitlab.com/user/duo_agent_platform/agents/foundational_agents/data_analyst/) to:
- Remove Beta designation and badges
- Update any Beta-specific disclaimers or limitations
- Ensure all features and capabilities are accurately documented
- Review and update any known issues or limitations sections
- Update availability/tier information if applicable
This is a GA readiness requirement for the Data Analyst Agent as tracked in https://gitlab.com/groups/gitlab-org/-/epics/20337.
issue