Tutorial: It's all connected in GitLab

What this post added

This post details how issues serve as the single source of truth, how to reference related issues, MRs, and comments using specific syntax (`#123`, `!123`, `$123`), and how merge requests can automatically close referenced issues upon merging using keywords like 'Closes #ID' or 'Fixes #ID'. It also covers the use of labels and milestones for categorization and target dates, and the `@mention` functionality for collaboration and assignment, which populates the 'Todos' list.