Support extra field regex in OpenAI API

[comaniac]

close #171

This PR adds an extra field regex in OpenAI protocols. Since OpenAI SDK 2.0, it allows arbitrary fields to be specified in the following approaches:

1. OpenAI SDK:

response = client.chat.completions.create(
    ...
    extra_body={"more_param": more_param_value},
)

2. CURL:

curl http:https://localhost:5000/v1/chat/completions?more_param=more_param_value ...

The extra parameter (i.e., regex) will be ignored by OpenAI models (e.g., gpt-3.5-turbo, gpt4, etc), but our SRT OpenAI API server will forward it correctly.

cc @remixer-dec