This checks the group features for sub epics support, if available the
allowSubEpics flag is propagated with the store and used in the epic
details component to hide/show the child epics icon.

This also adds the store to parent components specs that use
@vue/test-utils/mount.

See https://gitlab.com/gitlab-org/gitlab/-/issues/202172

This is part of multiple merge requests in order to reduce the risk of
breaking master

- Epic tree view on roadmap
- Async loading of children epic
- Tree view when filter is applied

Closes https://gitlab.com/gitlab-org/gitlab/issues/194303

- Mock milestones

Show milestones in Roadmap

- Add milestones list section to roadmap

Show milestones in Roadmap

- Milestones stack
- Popover on hover milestone
- Support for quarters filters
- Milestone title displays on roadmap

Show milestones in Roadmap

- Dashed lines on hover
- Fix popover alignment on milestone timeline bar

Add Milestones to Roadmap

- Milestones stack without overlapping for weeks and months
- Limited stacking on quarters, without overlap

Add Milestones to Roadmap

- Change empty roadmap conditions

Add milestones to roadmap

- Connect to graphql backend
- Refresh milestone dates

Add milestones to roadmap

- Style fixes
- Tests

Add Milestones in Roadmap

- Remove stacking of milestones

Add Milestones in Roadmap

- Introduce feature flag :milestones_in_roadmap

Add Milestones in Roadmap

- Implement feedback
- Use CSS utility classes
- Clean up CSS
- Migrate karma tests to jest

Add milestones to roadmap

- CSS tweaks
- Better styling for small milestones

This commit adds weight and progress information in roadmap epic bars

Makes first load of Roadmap page faster by batch
rendering only those epics which are visible on
viewport. This commit also cleans up Roadmap by
using CSS instead of JS to set component sizes.

Makes Roadmap timeline dynamic to be always
scrollable on any screen size.
Fetches new epics as user scrolls into past or future and renders it.

Signed-off-by: Rémy Coutable <remy@rymai.me>