Add sequence post processor (#771)
* Add `Sequence` PostProcessor
Required by https://huggingface.co/meta-llama/Meta-Llama-3-8B-Instruct/
* Support `return_token_type_ids`
* Add llama3 tokenizer to unit tests
* Add test for allowing user to request for token type ids
* Add JSDoc
* Update generate_tests.py
