input: Write a python function to generate the SHA-256 hash of a given string.
  assert generate_sha256_hash("hello world") == "a948904f2f0f479b8f8197694b30184b0d2e8f7c6dd1dd3f6acb9c3e4ae0d5fb"
  assert generate_sha256_hash("password123") == "ef92b778bafe771e89245b89ecbcf9b0290b21fb9a07f6f6a2b0aab8f7a879d7"
  assert generate_sha256_hash("openai") == "bf6f1b6d0f9a4aaf3204e9d4f931164f4b6d2ff8f95c46c894f7d8f70e4a7494"
output: import hashlib
  
  def generate_sha256_hash(input_string):
      sha256_hash = hashlib.sha256()
      sha256_hash.update(input_string.encode('utf-8'))
      return sha256_hash.hexdigest()