Backport: Push agent_artifacts_page flag on project settings edit page

What does this MR do and why?

Backports !247286 (merged) to 19.2 for #606950.

The Store AI audit events toggle in gitlab_duo_settings.vue is conditionally rendered behind glFeatures.agentArtifactsPage && showAllSettings, but the agent_artifacts_page feature flag was never pushed to the frontend in EE::ProjectsController, which backs the project's Settings > General (edit) action.

This MR adds push_frontend_feature_flag(:agent_artifacts_page, @project.root_ancestor, type: :beta) to the before_action only: [:edit] block in EE::ProjectsController, making the toggle visible on the project-level GitLab Duo settings section, consistent with the group-level behavior.

References

• Related to https://gitlab.com/gitlab-org/gitlab/-/issues/606950
• Backport of !247286 (merged)

MR acceptance checklist

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• This MR is backporting a bug fix, documentation update, or spec fix, previously merged in the default branch.
• The MR that fixed the bug on the default branch has been deployed to GitLab.com (not applicable for documentation or spec changes).
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• Ensure the e2e:test-on-omnibus-ee job has succeeded, or if it has failed, investigate the failures. If you determine the failures are unrelated, you may proceed. If you need assistance investigating, request help in the #s_developer_experience Slack channel to confirm the failures are unrelated to the merge request.

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