code: def artifact_event(
      self, name, filename, metadata=None, content_type=None
  ):
      self.save_file(filename, name)
      self.run_entry["artifacts"].append(name)
      self.save_json(self.run_entry, "run.json")
  
imports: import json
  import os
  import os.path
  import re
  from typing import Optional
  from sacred.commandline_options import cli_option
  from sacred.dependencies import get_digest
  from sacred.observers.base import RunObserver
  from sacred.serializer import flatten
  from sacred.utils import PathType
label_desc: Use image node_id 20 for calling the GoogleCloudStorageObserver obj's underlying member method code with example usage: obj.artifact_event(name, filename, metadata, content_type) without return types