Establish an ExportResult object to return from simplified functions

[mferrera]

TODO: needs refinement and maturation

We can and should return an object from the simplified export functions. This object will be useful for QC/information, for testing, for capturing information that may come in the future regarding sumo or upload status, and potentially for use cases we are not yet aware of.

A minimum viable product can look like this:

@dataclass
class ExportResultItem:
    relative_path: Path
    absolute_path: Path

# fmu.dataio.export.ExportResult ?
@dataclass
class ExportResult:
    items: list[ExportResultItem]

A simple use case for users is to print the location and names of exported files.

result = export_something()
for item in result.items:
    print(item.relative_path)  # => "path/to/file.type"

# Or, provide a method
result.print_filepaths()