Change HttpClientBase.ExecutePost to match upstream better and drop Newtonsoft.Json dependency

[AnastasiaJacson]

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Summary of the changes (Less than 80 chars)
Changed the HttpClientBase.ExecutePost to accept any kind of HttpContent and removed Newtonsoft Nuget reference.

Fixes #1176 (in this specific format)

Description

Changed the HttpClientBase.ExecutePost to accept any kind of HttpContent and removed Newtonsoft Nuget reference. Now it is not dependent on Newtonsoft.Json and better matches the upstream (see).

[paulirwin]

Hi @AnastasiaJacson - thanks for this PR! Unfortunately we have a little bit of a conflict as some of the work for this was done in #1182. I'm going to see what I can do to balance the work between these so that both can be merged. My current thinking is I'll work on merging this one first, then work with @NehanPathan to update #1182 since it touches on some different aspects. Thanks!

[paulirwin]

Thanks for this PR. Since you enabled edits by maintainers, I went ahead and did some minor cleanup of HttpClientBase and HttpReplicator that inherits from it. Some comments were no longer relevant with this PR, and the classes in general just needed some cleanup.

I also removed the Newtonsoft.Json dependency version from .build/dependencies.props since that is no longer needed.

[AnastasiaJacson]

Thanks! Yeah, that cleanup helped with code clarity)