vLLM NemoTokenizerGroup bugfix
FYI @HuiyingLi  I'm closing this as it's covered by https://github.com/NVIDIA/NeMo/pull/10697
# What does this PR do ?

For `NemoTokenizerGroup` in the base class [BaseTokenizerGroup](https://github.com/vllm-project/vllm/blob/v0.5.3/vllm/transformers_utils/tokenizer_group/base_tokenizer_group.py#L13-L17)  from vLLM there is an abstract `from_config` method that needs to be implemented. This change mocks the implementation to make `scripts/deploy/nlp/deploy_vllm_triton.py` functional.

There error fixed here is:
```
INFO 09-27 15:02:31 llm_engine.py:176] Initializing an LLM engine (v0.5.3) with config: model='/tmp/tmpioclfxxh', speculative_config=None, tokenizer=None, skip_tokenizer_init=False, tokenizer_mode=auto, revision=None, rope_scaling=None, rope_theta=None, tokenizer_revision=None, trust_remote_code=False, dtype=torch.bfloat16, max_seq_len=512, download_dir=None, load_format=<class 'nemo.export.vllm.model_loader.NemoModelLoader'>, tensor_parallel_size=1, pipeline_parallel_size=1, disable_custom_all_reduce=False, quantization=None, enforce_eager=False, kv_cache_dtype=auto, quantization_param_path=None, device_config=cuda, decoding_config=None, observability_config=None, seed=0, served_model_name=/data/export/LLAMA2-7B-fp8-sft.nemo, use_v2_block_manager=False, enable_prefix_caching=False)
ERROR 09-27 15:02:31 deploy_vllm_triton.py:169] An error has occurred while setting up or serving the model. Error message: An error has occurred during the model export. Error message: Can't instantiate abstract class NemoTokenizerGroup with abstract method from_config
```

CC @apanteleev 

**Collection**: NLP

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# Additional Information
* Related to https://github.com/NVIDIA/NeMo/pull/9381
