Feature(MInference): support llama 3.1

[Huiqiang Jiang (iofu728)]

What does this PR do?

• Support meta-llama/Meta-Llama-3.1-8B-Instruct;
• Fixes is_flash_attn_2_available issue;

Before submitting

• This PR fixes a typo or improves the docs (you can dismiss the other checks if that's the case).
• Was this discussed/approved via a Github issue? [ToDo]: V0.1.5 Iteration Plan #27
• Did you make sure to update the documentation with your changes?
• Did you write any new necessary tests?

Who can review?

Huiqiang Jiang (@iofu728)