Fix changelog example
What does this MR do and why?
The documentation for changelogs references the GitLab developer documentation in a few places which is somewhat misleading (as we have a custom changelog template configured).
When I first read the docs I thought we were constrained by default to the changelog categories used by the GitLab project, but this is not the case.
This MR removes the references to the GitLab developer docs.
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Edited by Lee Tickett