input: Write a python function to format a JSON string with proper indentation.
  assert format_json('{"name": "John", "age": 30, "city": "New York"}') == '{\n    "name": "John",\n    "age": 30,\n    "city": "New York"\n}'
  assert format_json('[{"name": "John", "age": 30, "city": "New York"}, {"name": "Jane", "age": 25, "city": "Chicago"}]') == '[\n    {\n        "name": "John",\n        "age": 30,\n        "city": "New York"\n    },\n    {\n        "name": "Jane",\n        "age": 25,\n        "city": "Chicago"\n    }\n]'
output: import json
  
  def format_json(json_string):
      parsed = json.loads(json_string)
      return json.dumps(parsed, indent=4)