Update Import/Export ObjectBuilder to not use Project.transaction

What does this MR do and why?

This MR fixes cross-DB transaction in Project Import/Export.

Instead of wrapping object creation in Project.transaction we can just wrap it in transaction of a class of the object that is being created. This way no cross-db exception is raised.

Additionally, update Group ObjectBuilder to remove Group.transaction in case we move group data into a separate database.

Mentions #350091 (closed)

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