Creating a dedicated package for iframe API typings

If users are willing to use Typescript to develop scripts for maps, they will need typings for the `WA` object.
This commit creates a new package (@workadventure/iframe-api-typings) that contains only the `iframe_api.d.ts` file.

The file is generated from the build of the front and isolated in this package.
This is necessary because the iframe_api.js file is supposed to always be loaded from WorkAdventure directly (and there is no @workadventure/iframe-api package and there will never be one)

front/packages/iframe-api-typings/package.json

@@ -0,0 +1,13 @@
+{
+  "name": "@workadventure/iframe-api-typings",
+  "version": "1.2.0",
+  "description": "Typescript typings for WorkAdventure iFrame API",
+  "main": "iframe_api.js",
+  "types": "iframe_api.d.ts",
+  "repository": "https://github.com/thecodingmachine/workadventure/",
+  "author": "David Négrier <d.negrier@thecodingmachine.com>",
+  "license": "MIT",
+  "publishConfig": {
+    "access": "public"
+  }
+}