input: Write a python function to convert a given string into its Base 64 representation.
  assert str_to_base64('Welcome to the world of programming!') == 'V2VsY29tZSB0byB0aGUgd29ybGQgb2YgcHJvZ3JhbW1pbmch'
  assert str_to_base64('Hello, World!') == 'SGVsbG8sIFdvcmxkIQ=='
  assert str_to_base64('Python is awesome!') == 'UHl0aG9uIGlzIGF3ZXNvbWUh'
output: def str_to_base64(s):
      import base64
      return base64.b64encode(s.encode()).decode()