Add dataset attachment to objects instead of collections when parsing

[JosePizarro3]

Useful if files are to be attached to objects instead of the collection where these are generated (e.g., when attaching data or plots)

[JosePizarro3]

Adding something like this in bam_masterdata.metadata.entities.py:ObjectType:

    @property
    def dataset(self):
        pass

    def add_dataset(self, file):
        pass

And modifying the corresponding run_parser() logic to only store in the attached_object and not in the collection