Add ESM Entrypoint with gen-esm-wrapper

[Jitesh Dhakshinamoorthy]

https://www.npmjs.com/package/gen-esm-wrapper

{
  "exports": {
    ".": {
      "require": "./index.js",
      "import": "./dist/output.mjs"
    },
    "./": "./"
  },
  "scripts": {
    "build": "gen-esm-wrapper . ./dist/output.mjs",
  },
}

[Jitesh Dhakshinamoorthy]

Nevermind it is not required, since we export only one class