Filtered search support for Epics list page

What does this MR do?

Adds support for filtering & sorting Epics in Epics list page;

Epics can be sorted based on;

• Created date
• Last updated

Epics can be searched based on;

• Title or description
• Author

Why was this MR needed?

This MR makes Epics list page consistent with Issues and MRs page where we support searching and sorting based on certain parameters.

Screenshots

Default View	Sorted by Last Updated	Filtered by Title/Description	Filtered by Author

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
• 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

What are the relevant issue numbers?

Closes #4656 (closed)