update template to build an esm version of the lib by default

[AndersonSMed]

Right now, any created lib will be built by using umd, and therefore won't support esm by default. This issue is meant to explore and add this support by default so the developer doesn't need to do so.

webpack/webpack#14998
https://dev.to/jakobjingleheimer/configuring-commonjs-es-modules-for-nodejs-12ed