Add Source Map Explorer

[mikhael28]

Let's take a look at why there is a 234kb JS 'shared' among all Next generated pages. Let's add the source-map-explorer npm package, which I think needs a little bit of configuration for Next.js, and let's see if there are any absurdly large npm packages that might need to be replaced. Perhaps the Amplify 'API' package can be replaced with the 'core' module, I hear that their tree-shaking is much improved.

If working on this, please add functionality in, post screenshot of source map explorer results, and send PR with updated package.json and yarn commands.