"lint" command for flipper-pkg tool

Summary:
Implemented json schema for flipper plugin package.json and used it for validation in "flipper-pkg lint" command.

Nice thing about json schema is that it not only allows to validate json, but also can be referenced using "$schema" property in json so IDEs like VSCode can find it and use for code completion, validation and to show properties documentation. I'm going to deploy the schema as a part of documentation website so it can be referenced as https://fbflipper.com/schemas/plugin-package/v2.json.

Also the "$schema" field can be used instead of "specVersion" to determine the specification according to which the plugin is defined. E.g., if specification version 3 would be created, it will be described in schema https://fbflipper.com/schemas/plugin-package/v3.json, etc.

Reviewed By: passy

Differential Revision: D21228294

fbshipit-source-id: f21351e584ef936a7d6b314436448489691f83a6

desktop/plugins/network/package.json

@@ -1,7 +1,7 @@
 {
+  "$schema": "https://fbflipper.com/schemas/plugin-package/v2.json",
   "name": "flipper-plugin-network",
   "id": "Network",
-  "specVersion": 2,
   "flipperBundlerEntry": "index.tsx",
   "main": "dist/index.js",
   "title": "Network",