feat: add initial package.json and demo server scripts #9

[hhkaos]

• Created package.json for the arcgis-rest-js-samples project with necessary metadata and dependencies.
• Implemented get-package-json.js to read and parse package.json files from the packages directory.
• Added the run-demo-server.js to initialize a demo server using browser-sync, serving static files from the node_modules of the packages.