Fix roadmap filters for child epics

What does this MR do and why?

Related to #412302 (closed)

In roadmaps when applying a filter that matches a child epic but not its parent, the child is missing from the results. This happens because we filter epics by topLevelHierarchyOnly to prevent the following epics duplication:

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This MR introduces a new fix for the duplication bug that allows us to remove the topLevelHierarchyOnly argument from the GraphQL query.

Screenshots or screen recordings

Before	After

How to set up and validate locally

1. Open rails console and create a group with epics:

user = User.first
start_date = 1.month.ago
end_date = Date.today + 2.months
group = Group.create!(name: 'Group with Roadmap', path: 'roadmap_group1')
label = GroupLabel.create!(title: 'Pink', group: group)
parent_a = Epic.create!(title: 'Parent A', author: user, start_date: start_date, end_date: end_date, group: group)
child_a = Epic.create!(title: 'Child A', author: user, group: group, parent: parent_a)
subchild_a = Epic.create!(title: 'Subchild A', author: user, start_date: start_date, end_date: end_date, group: group, parent: parent_a)
parent_b = Epic.create!(title: 'Parent B', author: user, start_date: start_date, end_date: end_date, group: group)
child_b = Epic.create!(title: 'Child B', author: user, start_date: start_date, end_date: end_date, group: group, parent: parent_b, labels: [label])

2. Visit the group's roadmap and verify that epics are displayed correctly:

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3. Filter epics by the Pink label and verify that Child B is the only result:

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