input: Write a python function to encode a message using Caesar cipher.
  assert encode_message("hellohello", 3) == "khoorkhoor"
  assert encode_message("abcxyz", 3) == "defabc"
  assert encode_message("xyzabc", 1) == "yzaabcd"
output: def encode_message(message, shift):
      encoded_message = []
      for char in message:
          if 'a' <= char <= 'z':
              new_char = chr(((ord(char) - ord('a') + shift) % 26) + ord('a'))
              encoded_message.append(new_char)
      return ''.join(encoded_message)