input: Write a python function to send a GET request to the /add endpoint and return the sum of two numbers.
  assert add_numbers(3, 5) == '8.0'
  assert add_numbers(10.5, 4.5) == '15.0'
  assert add_numbers(-1, 1) == '0.0'
output: def add_numbers(a, b):
      import requests
      response = requests.get(f'http://example.com/add', params={'a': a, 'b': b})
      return response.text