Add package.json linter and general json linter

Add linter for JSON files and package.json
Add documentation for both linters in docs/developer/automated-testing.md

Co-authored-by: Dhruvansu Thakkar <dhruvanshuthakkar@gmail.com>
Co-authored-by: Rarity <dongermcdingdong@gmail.com>

Closes issue #42 (closed)