In this PR, I expose the JsonSerializerSettings in the ApiClient so that serialization customizations can be done. For example, in my specific use-case, I wanted to add additional Converters to change the way JSON was being deserialized back into the csharp classes.

Fixes #4241

I reviewed the comments made on this related PR #4466 and incorporated the feedback into this PR.

@mandrean (2017/08) @frankyjuang (2019/09) @shibayan (2020/02)

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