input: Write a python function to find Armstrong numbers in a given range.
  assert find_armstrong_numbers(1, 1000) == [1, 2, 3, 4, 5, 6, 7, 8, 9, 153, 370, 371, 407]
  assert find_armstrong_numbers(100, 999) == [153, 370, 371, 407]
  assert find_armstrong_numbers(1000, 9999) == [1634, 8208, 9474]
output: def find_armstrong_numbers(start, end):
      def is_armstrong(number):
          digits = list(map(int, str(number)))
          power = len(digits)
          return sum(digit ** power for digit in digits) == number
  
      armstrong_numbers = []
      for num in range(start, end + 1):
          if is_armstrong(num):
              armstrong_numbers.append(num)
      
      return armstrong_numbers