Group migration - Store Temporary Import Data

This is part of the Group Migration MVC.

It needs to be completed before group import: #249159 (closed) and probably #249152 (closed)

Goal

To create a record that can be used to store data that is used only for the Group migration.

For now, this is expected to be:

1. Authentication data for the source instance

Notes

From #249159 (comment 412850331)

Store credentials for use in background job, similar to project_import_data, but for Groups. Perhaps a new table should be added to store this information.

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