Draft: erp5_pdm: restrict acquisition of `variation` to some Portal Types

Some time ago, I encountered an issue while trying to configure Transformation with variations: all variations of the transformed object used as resource of the Transformation where configured as "Default Variations" on the child Transformation Transformed Resources.

It makes no sense since Transformation Transformed Resources have their own resource defined, so this commit restricts acquisition on variation to try and get rid of this issue while keeping everything else fully working.

Draft because it might need a few tries to get everything working.