Refactor Bamboo migration guide

What does this MR do and why?

Refactors the Bamboo migration documentation to align with GitLab's topic types and style guide.

Changes made

  • Improved structure: Organized content using concept-task pattern for better scannability.
  • Reduced link overload: Cut links from 30+ to 12 essential migration-focused links (8 in migration steps + 4 in related topics).
  • Enhanced code examples: Converted side-by-side comparisons to tabs for better user experience.
  • Streamlined content: Removed content not directly relevant to migration tasks.
  • Content reorganization: Migration planning questions, Bamboo context, and configuration examples are preserved but reorganized for better flow.

Review app

Link: https://docs.gitlab.com/upstream-review-mr-ee-201381/ci/migration/bamboo/

Screenshots or screen recordings

TOC before TOC after
Screenshot_2025-08-13_at_6.00.01_PM Screenshot_2025-08-13_at_7.31.51_PM
Edited by Lysanne Pinto

Merge request reports

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