feat: add chat template

[amd-youchen]

Motivation

support custom chat template as passed in arguments

Technical Details

python -m atom.entrypoints.openai_server \
  --model /mnt/md0/models/DeepSeek-V4-Flash-FP8 \
  --kv_cache_dtype fp8 \
  --gpu-memory-utilization 0.83 \
  --served-model-name DeepSeek-V4-Flash-FP8 \
  --chat-template "{% for message in messages %}{% if message['role'] == 'system' %}{{ message['content'] + '\n\n' }}{% elif message['role'] == 'user' %}{{ 'User: ' + message['content'] + '\n\n' }}{% elif message['role'] == 'assistant' %}{{ 'Assistant: ' + message['content'] }}{% endif %}{% endfor %}{% if add_generation_prompt %}{{ 'Assistant:' }}{% endif %}" \
  -tp 8

[github-actions]

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