Docs - Add missing Docker restore commands

What does this MR do?

Our Docker restore documentation https://docs.gitlab.com/ee/raketasks/backup_restore.html#restore-for-docker-image-and-gitlab-helm-chart-installations doesn't mention that we need to stop processes that may connect to the database before we actually perform the restore.

These steps are already in our Omnibus instructions https://docs.gitlab.com/ee/raketasks/backup_restore.html#restore-for-omnibus-gitlab-installations, so we should include them in our Docker instructions.

The purpose of this MR is to help prevent users running into #36405 (closed), which can be caused if Unicorn/Puma/Sidekiq are not shut down before a restore, according to #36405 (comment 301954869) and #36405 (comment 359208008)

I've tested these commands and they work as intended.

Related issues

Author's checklist (required)

• Follow the Documentation Guidelines and Style Guide.
• If you have developer access or higher (for example, GitLab team members or Core Team members)
  • Apply the documentation label, plus:
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Do not add the feature, frontend, backend, ~"bug", or database labels if you are only updating documentation. These labels will cause the MR to be added to code verification QA issues.

When applicable:

• Update the permissions table.
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• Add GitLab's version history note(s).
• Add the product tier badge.
• Add/update the feature flag section.
• If you're changing document headings, search doc/*, app/views/*, and ee/app/views/* for old headings replacing with the new ones to avoid broken anchors.

Review checklist

All reviewers can help ensure accuracy, clarity, completeness, and adherence to the Documentation Guidelines and Style Guide.

1. Primary Reviewer

• Review by a code reviewer or other selected colleague to confirm accuracy, clarity, and completeness. This can be skipped for minor fixes without substantive content changes.

2. Technical Writer

• Technical writer review. If not requested for this MR, must be scheduled post-merge. To request for this MR, assign the writer listed for the applicable DevOps stage.
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  • Add docs-only when the only files changed are under doc/*.
  • Add twdoing when starting work on the MR.
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3. Maintainer

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