Update by_parent filter in EpicsFinder

What does this MR do and why?

%15.11 Backport for !120480 (merged)

The MR updates the existing top_level_hierarchy_only filter to return epics that have parents outside the group hierarchy.

This change fixes a bug in Roadmap, where epics are missing from the expected result.

MR acceptance checklist

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• This MR is backporting a bug fix, documentation update, or spec fix, previously merged in the default branch.
• The original MR has been deployed to GitLab.com (not applicable for documentation or spec changes).
• This MR has a severity label assigned (if applicable).
• This MR has been approved by a maintainer (only one approval is required).
• Ensure the e2e:package-and-test-ee job has either succeeded or been approved by a Software Engineer in Test.

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