Removes and redirects remaining design docs without cells

What does this MR do?

❗ Migrates remaining design documents without cells (gitlab-com/content-sites/handbook!7051 - merged) is a MR dependency for this MR ❗ We should only merge this once the dependency has been deployed!

We are currently migrating the Architecture design documents from the gitlab project to the public handbook.

gitlab-com/content-sites/handbook!7051 (merged) adds all remaining design documents (without cells) to the handbook. See table on the migration issue). Now this MR removes the original documents from the gitlab repository and instead adds redirects to the handbook.

Excerpt from design docs table. These documents are in this MR.

Design document folder	Creation Date	Migrated?	Redirect?
modular_monolith	2023-05-22	🚧 Part of "rest MR" ❗ Open MRs !135802
ai_context_management	2023-06-03	🚧 Part of "rest MR" ❗ Merged MR !158265 (merged)
gitlab_steps	2023-08-23	🚧 Part of "rest MR" ❗ Open MRs !138092
ci_build_speed	2024-01-12	🚧
gitlab_duo_rag	2024-01-25	🚧
disaster_recovery	2024-01-29	🚧
cdot_plan_managment	2024-02-07	🚧
autoflow	2024-02-16	🚧
gitlab_rag	2024-02-20	🚧
custom_models	2024-03-29	🚧
gitlab_xray_rag	2024-04-23	🚧
duo_workflow	2024-05-17	🚧
pipeline_mini_graph	2024-05-27	🚧
epss	2024-06-19	🚧

Leaves out the folders database and database_scaling as these don't show up in the design documents list and don't have proper metadata. I'll add follow-up issues for these.

Technical Writing maintainer review

Once approved, please ask @phillipwells for the Technical Writing review, so we can merge this. Additionally, post this or a similar message to the #docs Slack channel for visibility and if someone else wants to jump in:

Hello everyone :wave: this is another removal and redirect MR for
the architecture design documents migration. [LINK TO MR]

Phillipp Wells can you or someone else from your team please review
and merge this? :bow: Thanks a lot in advance :slight_smile:

Migration issue: https://gitlab.com/gitlab-com/content-sites/handbook/-/issues/279

Related issues

gitlab-com/content-sites/handbook#279 (closed)

Author's checklist

• Optional. Consider taking the GitLab Technical Writing Fundamentals course.
• Follow the:
  • Documentation process.
  • Documentation guidelines.
  • Style Guide.
• If you're adding a new page, add the product availability details under the H1 topic title.
• If you are a GitLab team member, request a review based on:
  • The documentation page's metadata.
  • The associated Technical Writer.

If you are a GitLab team member and only adding documentation, do not add any of the following labels:

• ~"frontend"
• ~"backend"
• ~"type::bug"
• ~"database"

These labels cause the MR to be added to code verification QA issues.

Reviewer's checklist

Documentation-related MRs should be reviewed by a Technical Writer for a non-blocking review, based on Documentation Guidelines and the Style Guide.

If you aren't sure which tech writer to ask, use roulette or ask in the #docs Slack channel.

• If the content requires it, ensure the information is reviewed by a subject matter expert.
• Technical writer review items:
  • Ensure docs metadata is present and up-to-date.
  • Ensure the appropriate labels are added to this MR.
  • Ensure a release milestone is set.
  • If relevant to this MR, ensure content topic type principles are in use, including:
    • The headings should be something you'd do a Google search for. Instead of Default behavior, say something like Default behavior when you close an issue.
    • The headings (other than the page title) should be active. Instead of Configuring GDK, say something like Configure GDK.
    • Any task steps should be written as a numbered list.
    • If the content still needs to be edited for topic types, you can create a follow-up issue with the docs-technical-debt label.
• Review by assigned maintainer, who can always request/require the reviews above. Maintainer's review can occur before or after a technical writer review.