input: Write a python function to encode a string to base64.
  assert encode_to_base64("Hello World!") == b'SGVsbG8gV29ybGQh'
  assert encode_to_base64("Python") == b'UHl0aG9u'
  assert encode_to_base64("Encode this!") == b'RW5jb2RlIHRoaXMh'
output: import base64
  
  def encode_to_base64(s):
      return base64.b64encode(s.encode('utf-8'))