input: Write a function to find all words in a given text that start with the letter 'a' (case insensitive) using regular expressions.
  assert find_words_starting_with_a("An apple a day keeps the doctor away.") == ['An', 'apple', 'a', 'away']
  assert find_words_starting_with_a("Alice was beginning to get very tired of sitting by her sister on the bank.") == ['Alice']
  assert find_words_starting_with_a("All around the rugged rocks, the ragged rascal ran.") == ['All', 'around']
output: def find_words_starting_with_a(text):
      import re
      return re.findall(r'\b[aA]\w*', text)