Make empty state copy aware of applied filters in Epics list and Roadmap view

What does this MR do?

Makes empty state view subtext aware of filters applied on the page. This MR makes the behaviour consistent for Epics list page and Epic Roadmap page. This MR is follow-up of https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/5417.

Screenshots

Default Empty State

Epics List	Epic Roadmap

Filtered Search Empty State

Epics List	Epic Roadmap

Epic Roadmap Empty State (when no epics are in timeframe)

Does this MR meet the acceptance criteria?

• [ ] Changelog entry added, if necessary
• [ ] Documentation created/updated
• [ ] API support added
• Tests added for this feature/bug
• Review
  • Has been reviewed by UX
  • Has been reviewed by Frontend
  • [ ] Has been reviewed by Backend
  • [ ] Has been reviewed by Database
• EE specific content should be in the top level /ee folder
• Conform by the merge request performance guides
• Conform by the style guides
• Squashed related commits together
• Internationalization required/considered
• [ ] If paid feature, have we considered GitLab.com plan and how it works for groups and is there a design for promoting it to users who aren't on the correct plan
• [ ] End-to-end tests pass (package-qa manual pipeline job)

What are the relevant issue numbers?

#3729 (closed)