Add GDK-in-a-box documentation to contribute docs

What does this MR do?

Add steps from GDK-in-a-box doc in the gitlab-development-kit repo to suggest it as part of the contributor workflow.

To discuss:

• Treat the GDK repo as the single source of truth. Answers to these combined in: !144251 (comment 1765197776)
  • should the GDK docs direct users to this documentation?
  • is this the best place for this?
  • should other GDK docs be transcribed from where they are in the GDK repo to a better place in the GitLab documentation?
• Since "GDK-in-a-box" seems to work so much faster and better, should we make it the default and tuck the traditional GDK installation under a <details>-style component? or should that method go to some dedicated GDK documentation?
  • Maybe. But leaving it for now: !144251 (comment 1765198431)

Related issues

• Edit of original first_contribution doc: !142561 (merged)
• Single page to multi-page: !142742 (merged)

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.

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.