Issue sorting on Backlog should match Roadmap sorting

Summary

Currently on Next-gen Projects, the list of Epics on the Backlog view are sorted based on their IDs.

Meanwhile, Epics are sorted based on priority in the Roadmap view. Because of these 2 different factors, Epics on the Backlog view aren't sorted according to what is shown in the Roadmap which creates confusion.

Roadmap

Backlog

Proposed solution

Match the sorting on the Backlog view with what is displayed on the Roadmap view which is based on priority.