GitLab Migration - More fine-grained status for group bulk imports

Problem to solve

Per this comment, when migrating Groups in bulk, all top-level groups are imported in one bulk batch. This user experience is shown in this video.

This means that if we have group1, group2, and group3 on the page and click Import all - their statuses will always be in sync for all three groups. Even when all related imports for i.e. group1 are completed, the status for group1 will remain Importing... until all the other groups in the same batch are completed.

Proposed solution

It would be useful to have a more fine-grained status. This can be accomplished by either having separate statues for each group in the batch, or by having separate batches for the top-level groups.