fix(build): remove json files from nuget package content folders

[bkapustik]

Motivation

Checklist

• [x] Code follows coding conventions held in this repo
• [ ] Automated tests have been added
• [x] Tests are passing
• [ ] Docs have been updated (if applicable)
• [ ] Temporary settings (e.g. variables used during development and testing) have been reverted to defaults

[seangwright]

@michalJakubis I resolved a couple outstanding issues with the repo and validated that the NuGet package no longer contains the extra files (it still had 1 extra, unused JS file when I initially tested).

@bkapustik I noticed the nuget.config was changed in commit b8fde0a271eb1f07291f03fdc30deab6d1b7e587. The nuget.config is intentionally setup to allow for local testing of NuGet packages which helps us make sure the package is built correctly and includes all the required files.

However, I also saw there had been a line that was uncommented that should have been commented out, and it caused non-package local development to not work for you.

I fixed this and I also improved the documentation for local NuGet package testing.