add openai base url to OpenAIChatRuntime and AsyncOpenAIChatRuntime

[matt-bernstein]

update of #84

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 43.79%. Comparing base (fcd7eaf) to head (82aa8c6).
Report is 6 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #145      +/-   ##
==========================================
+ Coverage   43.76%   43.79%   +0.03%     
==========================================
  Files          40       40              
  Lines        1812     1813       +1     
==========================================
+ Hits          793      794       +1     
  Misses       1019     1019              

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Commit https://github.com/HumanSignal/infra/commit/4cd404bcd9ab8dc07459659560b1eed2c18caec4 is created.

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Commit https://github.com/HumanSignal/infra/commit/3c4ff56fa2362a66109e96bb002009922ec0f860 is created.

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Commit https://github.com/HumanSignal/infra/commit/62aaed24603f09b873f88a18663f9b08272b77cf is created.