Don't user issuable_sort cookie for epics collection

What does this MR do?

It fixes the error on epic list page by rewriting the IssuableCollections method that sets the sort param from a cookie.

Are there points in the code the reviewer needs to double check?

Why was this MR needed?

When a user sorted eg. issues by labels the sorting was stored in the cookie. This cookie was later used again by IssuableCollections which we use for epics too. But we don't support custom sorting for epics + not everything we support on issues/MRs is supported on epics (eg. labels are not yet supported)

Screenshots (if relevant)

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 #4114 (closed)