User Story mapping is a powerful way to visualize how people are using your product or feature holistically and organize individual stories to that journey. A story map can even be annotated to indicate which user stories need to be included in each release, making it a valuable tool for PMs and Designers to use during planning.
Much like a User Journey Map, a Story Map outlines a workflow and breaks it in to individual steps. Then, each story (which is likely issues, in GitLab's case), are organized around the individual steps in the workflow.
From there, the stories can be organized in priority ranking, or grouped in to milestones to make it easier to think about planning.
Here are some resources to learn more about story mapping: