Migrate Group Milestones with the Group

Problem to solve

For the Group Migration to be a viable solution for the users migrating Groups, we need to achieve parity with the Group Export/Import feature.

Proposed Solution

As part of the larger epic targeting parity with Group Export/Import, this issue adds Group Milestones to Group Migration.

query groupMilestones($full_path: ID!, $cursor: String) {
  group(fullPath: $full_path) {
    milestones(first: 100, after: $cursor, includeDescendants: false) {
      pageInfo {
        next_page: endCursor
        has_next_page: hasNextPage
      }
      nodes {
        title
        description
        state
        due_date: dueDate
        created_at: createdAt
        updated_at: updatedAt
      }
    }
  }
}

Documentation

Following documentation should be updated with the fields added in this issue:

• User docs: https://docs.gitlab.com/ee/user/group/import/
• Dev docs: https://docs.gitlab.com/ee/development/bulk_import.html