input: Write a function to generate SHA-256 hash of a given input string.
  assert generate_sha256('ExampleString') == 'f5d1278e8109edd94e1e4197e04873b5d36f3a8bfa3b8c3c9e1c9b7f2e4e23d1'
  assert generate_sha256('hello') == '2cf24dba5fb0a30e26e83b2ac5b9e29e1b161e5c1fa7425e73043362938b9824'
  assert generate_sha256('world') == '486ea46224d1bb4fb680f34f7c9bbdd8e4074d9a1b4135f2aa5e5d5649a5a802'
output: def generate_sha256(input_string):
      import hashlib
      sha256_hash = hashlib.sha256(input_string.encode()).hexdigest()
      return sha256_hash