Draft: Auto-merge page updates

What does this MR do?

This merge request updates https://docs.gitlab.com/ee/user/project/merge_requests/merge_when_pipeline_succeeds.html in a few ways:

• !145872 (63dde8c6) swaps the order of the subheadings "Merge when checks pass" and "Merge when pipeline succeeds". Purely to help minimize merge conflicts.
• !145872 (b54bff50) takes the various API merge statuses, and blends them together into a more colloquial description of the checks run by this feature. It doesn't outright say that enabling one enables the other. Perhaps it should? 🤔

Related issues

• Related to Docs follow-up: Merge When Checks Pass (#440696 - closed) and may even close it
• Related to Document new Merge When Checks Pass (!143479 - merged) where these changes were requested but not done
• Related to Document new Merge When Checks Pass (#431449 - closed)
• Related to Plan for changes from 'auto_merge_labels_mr_wid... (technical-writing#782)
• Related to [Feature flag] Rollout of `merge_when_checks_pass` (#412995)
• Related to [Feature flag] Rollout of `additional_merge_whe... (#424784)

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 tier badge 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.