Add changelog page to left navigation

In my initial proposal here, I've added https://docs.gitlab.com/ee/user/project/changelog.html to the left nav in: Use GitLab > Deploy and release your application. I'm not convinced this is right. I could make a case for Use GitLab > Plan and track work, but other possibilities exist, too. What I've added here is a first guess, and I'm amenable to suggestions if someone has a strong opinion.

Add navigation item to global navigation

• Link to the merge request that introduced the new page: gitlab!109656 (merged)
• Give the MR a descriptive title.
• Optional. Link to the new page: https://docs.gitlab.com/ee/user/project/changelog.html