Add support for auto-expanding Roadmap timeline on horizontal scroll

What does this MR do?

This MR adds support for expanding Roadmap timeline by prepending/appending timeframe items on horizontal scroll.

Roadmap

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• [ ] Documentation created/updated
• Tests added for this feature/bug
• Tested in all supported browsers
• Conforms to the code review guidelines
• Conforms to the merge request performance guidelines
• Conforms to the style guides
• [ ] Conforms to the database guides
• ~~[ ] Link to e2e tests MR added if this MR has Requires e2e tests label. See the Test Planning Process.~~
• EE specific content should be in the top level /ee folder
• For a paid feature, have we considered GitLab.com plans, how it works for groups, and is there a design for promoting it to users who aren't on the correct plan?
• Security reports checked/validated by reviewer

Closes #7325 (closed) https://gitlab.com/gitlab-org/gitlab-ee/issues/9119