Fix the UX of the "Infrastructure" documentation pages
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### Problem to solve
As a GitLab user, I need excellent documentation so that I can learn more about GitLab infrastructure oriented features.
### Intended users
* [Delaney (Development Team Lead)](https://about.gitlab.com/handbook/marketing/product-marketing/roles-personas/#delaney-development-team-lead)
* [Sidney (Systems Administrator)](https://about.gitlab.com/handbook/marketing/product-marketing/roles-personas/#sidney-systems-administrator)
* [Sam (Security Analyst)](https://about.gitlab.com/handbook/marketing/product-marketing/roles-personas/#sam-security-analyst)
* [Allison (Application Ops)](https://about.gitlab.com/handbook/marketing/product-marketing/roles-personas/#allison-application-ops)
* [Priyanka (Platform Engineer)](https://about.gitlab.com/handbook/marketing/product-marketing/roles-personas/#priyanka-platform-engineer)
and our buyer personas.
### User experience goal
- Create a new landing page for [the Infrastructure docs](https://docs.gitlab.com/ee/user/project/clusters/)
- Fix the menu to make it easy to find subpages based on the user's job
### Proposal
### Iteration 1
- [ ] Come up with an information architecture of the final output
- [ ] Rewrite the Infrastructure docs landing page
- [ ] Create new, follow-up issues for missing pages
### Iteration 2
- [ ] Schedule the new issues from Iteration 1
### Further details
<!-- Include use cases, benefits, goals, or any other details that will help us understand the problem better. -->
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