input: Write a python function to split a paragraph into unique words sorted alphabetically.
  assert split_and_sort_unique_words("This is a sample paragraph.") == "a, is, paragraph., sample, This"
  assert split_and_sort_unique_words("hello world hello") == "hello, world"
  assert split_and_sort_unique_words("Python is great. Python is fun.") == "fun., great., is, Python"
output: def split_and_sort_unique_words(paragraph):
      words = paragraph.split()
      unique_words = sorted(set(words))
      return ', '.join(unique_words)