CTRT Part 1: Registering runners page

What does this MR do?

Part 1 of CTRT edits for Registering runners page:

• Restructures the page into new sections:
  • Register with a runner authentication token.
  • Register with a runner registration token (deprecated).
  • Register with a one-line command.
• Adds tabs for registration commands for each operating systems (Linux, macOS, etc).
• Adds a Troubleshooting section.

Before: https://docs.gitlab.com/runner/register/

After: https://main-runner-4371.docs.gitlab-review.app/runner/register

---

This MR focuses mainly on restructuring. Follow up MRs will address:

• Edits for:
  • Sections about one-line registration commands.
  • # [[runners]] configuration template file section and title.
  • Troubleshooting section.
  • Intro paragraph under H1.
• Merge one-line registration sections into task topics for registering with authentication token and registration token.
• Additional context about token types for registration.

Related issues

• #36882 (closed)
• technical-writing#839 (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 or changing the main heading of the page (H1), ensure that the product tier badge is added.
• 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 above reviews. Maintainer's review can occur before or after a technical writer review.