Group Import/Export has epic labels association missing

Summary

When Importing a group that has epics with labels using Group Import/Export imported epics lose their labels association.

Steps to reproduce

1. Export a group with epics that have labels on them
2. Import a group and observe imported epics
3. Verify epics do not have labels associated

What is the current bug behavior?

Epics do not have labels preserved.

What is the expected correct behavior?

Epics should have labels preserved.

Possible fixes

Update https://gitlab.com/gitlab-org/gitlab/-/blob/master/lib/gitlab/import_export/group/import_export.yml to include labels in epics association.

- label_links:
  - :label