input: Write a python function to find all the indices of a given string in an array of strings.
  assert find_string(["hello", "world", "hello", "world"], "world") == [1, 3]
  assert find_string(["apple", "banana", "cherry", "banana"], "banana") == [1, 3]
  assert find_string(["a", "b", "a", "b", "a"], "a") == [0, 2, 4]
output: def find_string(arr, target):
      return [index for index, value in enumerate(arr) if value == target]