Added list type toggle to merge request dashboard

What does this MR do and why?

Adds a toggle to switch between role based and action based list rendering on the merge request dashboard.

References

Please include cross links to any resources that are relevant to this MR. This will give reviewers and future readers helpful context to give an efficient review of the changes introduced.

• https://gitlab.com/gitlab-org/gitlab/-/issues/519717

MR acceptance checklist

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Screenshots or screen recordings

How to set up and validate locally

• Enable merge_request_dashboard feature flag
• Enable mr_dashboard_list_type_toggle feature flag
• Visit https://gdk.test:3000/dashboard/merge_requests