input: Write a python function to replace all occurrences of a target word in a sentence with a replacement word.
  assert search_replace("The quick brown fox jumps over the lazy dog", "quick", "slow") == "The slow brown fox jumps over the lazy dog"
  assert search_replace("Hello world, welcome to the world of Python", "world", "universe") == "Hello universe, welcome to the universe of Python"
  assert search_replace("Repeat repeat repeat", "repeat", "echo") == "Repeat echo echo"
output: def search_replace(sentence, target, replacement):
      return sentence.replace(target, replacement)