Introduces Group import feature with ndjson

#212327 (closed)

What does this MR do?

To improve performance, and the memory footprint of the group import feature, the ability to import a group-tree in the ndjson format is being introduced. This feature is behind a feature flag (:group_import_export_ndjson) for now.

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Originally all the effort to enable ndjson on for Group Import/Export feature was done in one MR, which endup being too big. @ayufan then suggested to split that work on smaller MRs to make the work easier to review.

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Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation (if required)
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• Style guides
• Database guides
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Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers
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Security

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