Group migration E2E test - Epic migration

Validate epics are migrated correctly with all the sub items:

• title
• description
• state (open / closed)
• start date
• due date
• confidentiality
• labels (Introduced in 13.9)
• parent epic (Introduced in 13.9)
• emoji award (Introduced in 13.9)
• author (Introduced in 13.9)

Not tested:

• ❌ epic order on boards - introduces significant complexity testing e2e level
• ❌ events (Introduced in 13.10) - since events are not tied to object but user (doc) and we are using same user and same instance, it makes it rather inconvenient to validate