Redact data-usage page in prep for deletion

What does this MR do?

!163208 isn't ready yet, but as part of that work, doc/user/project/merge_requests/reviews/data_usage.md was to be redacted + converted into a redirect, because the feature is gone with no replacement.

As part of prepping for !163208, I took the page out of the left nav a few weeks ago. !163208 hadn't merged yet, so the left-nav removal looked like a mistake, because the page still existed. It was re-added to the nav.

Let's redact this page + turn into a redirect, separately from !163208. This will ensure that when I take the page out of the left nav again shortly, it's obviously intentional.

EDIT: Changed plan to add metadata to the page to prevent it from being re-added to the nav. The page will be removed as part of the related MR at a later date.

(FYI, @phikai)

Related issues

• Related to Add documentation for new merge request reviewe... (!163208) which was originally going to contain the redaction
• Related to Remove data-usage page from nav (gitlab-docs!5038 - merged) where we took it out of the left nav (the first time) 😜
• Related to Add missing pages to nav (gitlab-docs!5075 - merged) where it was restored, because others weren't aware that the removal from the left nav was intentional
• Related to Removes the data-usage page for realsies! (gitlab-docs!5137 - merged) where we'll take it out of the left nav one last time

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.