Feat: Add ai legal disclaimer to new agent session and new flow trigger pages

What does this MR do and why?

This MR does the following:

1. Adds the Beta experiment badge to the Automate page headers: Agent sessions and Flow triggers.
2. Adds legal disclaimer to the bottom of the sub-children pages: Agent sessions > New and Flow triggers > New.
3. Adds y-axis border to agent sessions list since this no longer hidden under a FF and to help separate all the white spacing gaps.
4. Fix margin on Agent sessions > New page that made it not align with the Flow triggers > New page.

Related Issue: https://gitlab.com/gitlab-org/gitlab/-/issues/562399

References

Screenshots or screen recordings

Page	Before	After
Agent sessions
Agent sessions > New
Flow triggers
Flow triggers > New

How to set up and validate locally

1. Make sure you have AI features enabled https://docs.gitlab.com/development/ai_features/
2. Turn on the following feature flags: duo_workflow, duo_workflow_in_ci, and ai_flow_triggers
3. Navigate to a project with that has AI features enabled (see Step 1).
4. In the left side panel, you will see Automate with a tanuki icon.
5. Click the dropdown and select Agent sessions. This will load your agent sessions in that project.
6. If you need to populate flows, run the rake task for your project (ee/lib/tasks/gitlab/duo_workflow/duo_workflow.rake) bundle exec rake "gitlab:duo_workflow:populate[50,20,1,gitlab-duo/test]".
7. Validate session items now have a border. Validate there is now a page header/title along with the experiment tag labeled Beta.
8. Click on the New session button on the top right of the page.
9. When on the New session page, validate the disclaimer appears at the bottom and that the page has the appropriate margins.
10. In the left side panel, under the Automate dropdown select Flow triggers. This will load your flow triggers in that project.
11. Validate there is now an experiment tag labeled Beta next to the page header.
12. Click on the Create flow trigger button on the top right of the page.
13. When on the Create flow trigger page, validate the disclaimer appears at the bottom.

MR acceptance checklist

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Related to #562399