docs: Add a lockfile step to the registry revert and match quotes

Andrew Dunnrequested to merge
docs/registry-revert-lockfile-quotes into master

What does this MR do?

In the review of !249940, @z_painter asked whether "Revert to object storage metadata" still works once database-in-use exists, and noted that two sections double-quote "prefer" and "false". This MR covers both.

On 19.4.1 with object storage, the registry restarts in a loop on registry metadata database in use without the new step. With it, the procedure as written starts the registry once, on legacy metadata, with the pre-migration images.

Revert procedure

flowchart TD
    restore["gitlab-backup restore of a backup from before the migration"] --> storage{"Registry storage"}
    storage -->|"Local file system: the restore replaces the lockfiles"| config["'enabled' => false, then gitlab-ctl reconfigure"]
    storage -->|"Object storage: database-in-use stays in the bucket"| delete["Delete database-in-use from the bucket (new step)"]
    delete --> config
    config --> legacy["Registry starts on legacy metadata"]

"Default configuration" and "New installations" now use 'prefer' and a boolean false, matching !249940 (merged) and the revert section. Omnibus applies its default only when the value is unset, so a boolean false holds.

Related issues

Related to !249940 (merged).

Author's checklist

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

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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.
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      • 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.
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This MR was prepared with assistance from Claude Code. The revert behavior was observed on a GitLab 19.4.1 instance, the Omnibus default was read from the linked source, and the page passes Vale and markdownlint at the CI versions.

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