Fix Baichuan2-7B-Chat

[firebook]

This PR fix Baichuan2-7B-Chat model, use "ROPE" instead of "ALIBI" when load Baichuan2-7B-Chat model

relate issue: #1561 #1092 #1085

before fix:

curl http://127.0.0.1:8080/v1/completions \
> -H "Content-Type: application/json" \
> -d '{
>     "model": "Baichuan2-7B-Chat",
>     "prompt": "<reserved_106>How are you?<reserved_107>",
>     "temperature": 0,
>     "max_tokens": 300,
>     "stream": false
> }'
{
"id":"cmpl-a6ae13d369714779a2e65d8220e00413",
"object":"text_completion","created":3634794,"model":"Baichuan2-7B-Chat",
"choices":[{"index":0,"text":"As a language model, I am a language agent","logprobs":null,"finish_reason":"stop"}],
"usage":{"prompt_tokens":6,"total_tokens":17,"completion_tokens":11}
}

after fix:

curl http://127.0.0.1:8080/v1/completions -H "Content-Type: application/json" -d '{
    "model": "Baichuan2-7B-Chat",
    "prompt": "<reserved_106>How are you?<reserved_107>",
    "temperature": 0,
    "max_tokens": 300,
    "stream": false
}'
{
"id":"cmpl-cadc09ae25294917a9e2d1d986475957",
"object":"text_completion","created":3635047,"model":"Baichuan2-7B-Chat",
"choices":[{"index":0,"text":"I'm fine, thank you! How about you?","logprobs":null,"finish_reason":"stop"}],
"usage":{"prompt_tokens":6,"total_tokens":19,"completion_tokens":13}}

[simon-mo]

Thank you for the fix!

[WoosukKwon]

Can we make this into two separate lines? This doesn't look good stylistically 😢

[simon-mo]

i think this is how yapf wanted it. but once we switch to black formatting this will be waaaaaaay better

[simon-mo]

you can stamp this PR: #1688 to make it happen!