input: Write a python function to find a specified value in a 2-dimensional array.
  assert find_value_in_2d_array([[1, 2, 3], [4, 5, 6], [7, 8, 9]], 5) == [1, 1]
  assert find_value_in_2d_array([[1, 2, 3], [4, 5, 6], [7, 8, 9]], 10) == None
  assert find_value_in_2d_array([['a', 'b', 'c'], ['d', 'e', 'f'], ['g', 'h', 'i']], 'e') == [1, 1]
output: def find_value_in_2d_array(array, value):
      for i, row in enumerate(array):
          for j, element in enumerate(row):
              if element == value:
                  return [i, j]
      return None