chore(core): Update package.json to support esm

Author: dasuni-30

packages/core/package.json

@@ -2,7 +2,7 @@
   "name": "@asgardeo/js",
   "version": "0.1.2",
   "description": "Framework agnostic JS for Asgardeo or Identity Server",
-  "main": "dist/cjs/index.js",
+  "main": "dist/esm/index.js",
   "module": "dist/esm/index.js",
   "umd": "dist/umd/index.js",
   "types": "dist/index.d.ts",