input: Write a python function to retrieve JSON data from a URL and convert it into a pandas DataFrame.
  assert isinstance(retrieve_and_convert_to_df("http://example.com/products"), pd.DataFrame)
  assert not retrieve_and_convert_to_df("http://example.com/products").empty
output: def retrieve_and_convert_to_df(url):
      import requests
      import pandas as pd
  
      response = requests.get(url)
      data = response.json()
      df = pd.DataFrame(data)
      return df