input: Write a python function to join two strings with " and " as the separator.
  assert join_strings("Apples", "Oranges") == "Apples and Oranges"
  assert join_strings("Hello", "World") == "Hello and World"
  assert join_strings("Python", "Programming") == "Python and Programming"
output: def join_strings(str1, str2):
      return f"{str1} and {str2}"