Add in Chat Completion + ML Feature (#5)

**Summary**
This PR adds in chat completion so that it can be used by the Azure Open
AI Endpoint.

---------

Co-authored-by: Sophia Chen <sophia.six.chen@gmail.com>

OpenAI.WinRT.nuspec

@@ -2,7 +2,7 @@
 <package >
   <metadata>
     <id>OpenAI.WinRT</id>
-    <version>0.0.9</version>
+    <version>0.0.10</version>
     <title>OpenAI.WinRT</title>
     <authors>Alexander Sklar</authors>
     <requireLicenseAcceptance>false</requireLicenseAcceptance>

OpenAIClient.cpp

@@ -452,7 +452,7 @@ namespace winrt::OpenAI::implementation
         ));
 
       auto content = winrt::HttpStringContent(requestJson, winrt::UnicodeEncoding::Utf8, L"application/json");
-      auto uri = Windows::Foundation::Uri{ gpt35turboEndpoint };
+      auto uri = m_useBearerTokenAuthorization ? Windows::Foundation::Uri{ gpt35turboEndpoint } : CompletionUri();
       auto response = co_await m_client.PostAsync(uri, content);
       auto responseJsonStr = co_await response.Content().ReadAsStringAsync();
       statusCode = response.StatusCode();