code: def _insert_manifest_item(configurator, key, item):
      
      with _open_manifest(configurator) as f:
          manifest = f.read()
      if item in ast.literal_eval(manifest).get(key, []):
          return
      pattern = """(["']{}["']:\\s*\\[)""".format(key)
      repl = """\\1\n        '{}',""".format(item)
      manifest = re.sub(pattern, repl, manifest, re.MULTILINE)
      with _open_manifest(configurator, "w") as f:
          f.write(manifest)
docs: Insert an item in the list of an existing manifest key