Drop Newtonsoft and replace with System.Text.Json (v14.09)

[iJungleboy]

I'm submitting a ...
[x] feature request

...about
[x] APIs like REST
[x] other / unknown

Current behavior

Historically 2sxc used Newtonsoft as it was just included in DNN and Oqtane. But moving forward, we want to reduce dependencies.

So we wish to only use System.Text.Json. This is a very large change!

Your environment

• 2sxc version(s): 14.08