Add session_details_right_rail feature flag

What does this MR do and why?

Adds the session_details_right_rail WIP feature flag and pushes it to the frontend via the DuoAgentsPlatformController before_action.

The flag controls rendering of agent session detail attributes in a right-rail panel on the project page view (excludes the side panel view) using GlAttributeList organized into sections.

Files changed:

• ee/app/controllers/projects/duo_agents_platform_controller.rb — pushes the new feature flag to the frontend
• ee/config/feature_flags/wip/session_details_right_rail.yml — feature flag definition
• ee/spec/requests/projects/duo_agents_platform_controller_spec.rb — verifies the flag is pushed to the frontend

References

• Work Item: #609575
• Task: #622008 (closed)
• FF Work Item: #622809
• Original MR: !251734 (merged)

Screenshots or screen recordings

Before	After
N/A (feature flag only)	N/A (feature flag only)

How to set up and validate locally

1. Enable the feature flag in rails console:

   Feature.enable(:session_details_right_rail, current_user)

2. Visit a project's Automate page (agent sessions view).
3. Verify sessionDetailsRightRail is present in the page's gon data.

MR acceptance checklist

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