Refactor code in groups' importer and exporter

What does this MR do?

In this MR we refactor a little bit the groups' importer/exporters. All these changes will be used later in !51873 (merged).

This is just an iterative MR splitting the work.

Does this MR meet the acceptance criteria?

Conformity

• Code review guidelines
• Merge request performance guidelines
• Style guides
• Separation of EE specific content

Refs #207886 (closed)