Add a file as an artifact.

        In Sacred terminology an artifact is a file produced by the experiment
        run. In case of a MongoObserver that means storing the file in the
        database.

        This function can only be called during a run, and just calls the
        :py:meth:`sacred.run.Run.add_artifact` method.

        Parameters
        ----------
        filename : str
            name of the file to be stored as artifact
        name : str, optional
            optionally set the name of the artifact.
            Defaults to the relative file-path.
        metadata: dict, optional
            optionally attach metadata to the artifact.
            This only has an effect when using the MongoObserver.
        content_type: str, optional
            optionally attach a content-type to the artifact.
            This only has an effect when using the MongoObserver.

def add_artifact(
            self,
            filename,
            name=None,
            metadata=None,
            content_type=None,
    ):
        """Add a file as an artifact.

        In Sacred terminology an artifact is a file produced by the experiment
        run. In case of a MongoObserver that means storing the file in the
        database.

        This function can only be called during a run, and just calls the
        :py:meth:`sacred.run.Run.add_artifact` method.

        Parameters
        ----------
        filename : str
            name of the file to be stored as artifact
        name : str, optional
            optionally set the name of the artifact.
            Defaults to the relative file-path.
        metadata: dict, optional
            optionally attach metadata to the artifact.
            This only has an effect when using the MongoObserver.
        content_type: str, optional
            optionally attach a content-type to the artifact.
            This only has an effect when using the MongoObserver.
        """
        assert self.current_run is not None, "Can only be called during a run."
        self.current_run.add_artifact(filename, name, metadata, content_type)