✨ Fix hierarchy, clarify Admin Area links

Why is this change being made?

This change adjusts the SaaS, Self-Managed and Dedicated Troubleshooting tables workflow to:

• fix the hierarchy so that Admin Area and Gitaly are at the same level as Auth and Geo
• link to information about the GitLab Rails console
• remove duplicate links to the Admin Area docs

This helps a bit with gitlab-com/gl-infra/gitlab-dedicated&212

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