Group Migration - Import Epics (MVC)

This is part of the Group Migration MVC.

It needs to be completed after group import: #249159 (closed)

Goal

To import epics when performing a group import using the new API based approach.

Future Iterations

• Complete the Epics migration: &5189 (closed)

Notes

From #249159 (comment 412850331)

Create Epic ETL Pipeline that imports epics into groups. We might need to have a source -> destination group id map in order to understand which group to save epic to. Or use other unique identifier. Another option would be to have Group + Epic pipeline combined into 1, but as the solution grows, we don't want to have 1 pipeline for everything, but have more modular approach that allows us swap or add new relations