Expand default Roadmap timeframe to enable horizontal scroll of timeline

What does this MR do?

This MR is follow-up on https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/9023.

It expands default timeframe based on available horizontal viewport size to enable timeframe scrolling which will then allow user to scroll around and keep on expanding Roadmap timeline.

• Changelog entry added, if necessary
• Documentation created/updated via this MR
• 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](https://about.gitlab.com/handbook/engineering/quality/test-engineering/).
• 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

#7325 (closed)