Support LoRA for Gemma

[Michaelvll]

I am getting the following error when loading a lora adaptor for Gemma model:

  python -u -m vllm.entrypoints.openai.api_server \
    --host 0.0.0.0 \
    --model google/gemma-7b \
    --enable-lora \
    --lora-modules quote=/artifacts \
    --max-model-len 1024 | tee ~/openai_api_server.log

ValueError: Model GemmaForCausalLM does not support LoRA, but LoRA is enabled. Support for this model may be added in the future. If this is important to you, please open an issue on github.