add extra_body in ChatCompletion

[matabeibei]

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[codecov]

Codecov Report

Attention: Patch coverage is 76.92308% with 6 lines in your changes missing coverage. Please review.

Project coverage is 99.32%. Comparing base (c4273cb) to head (ecd9794).

Files with missing lines	Patch %	Lines
chat.go	76.92%	2 Missing and 1 partial ⚠️
chat_stream.go	76.92%	2 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1054      +/-   ##
==========================================
- Coverage   99.59%   99.32%   -0.27%     
==========================================
  Files          34       34              
  Lines        2205     2229      +24     
==========================================
+ Hits         2196     2214      +18     
- Misses          6       10       +4     
- Partials        3        5       +2     

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