Setting to change which bundles are generated (client and/or server) [8pt]

[SantosGuillamot]

This is needed for AMP feature. For full context please check out the final Implementation proposal.

---

In some cases, like in AMP, we don't need to generate bundles for the client because the Google AMP framework forbids the use of external JavaScript.

It will be managed by a new site setting on the frontity.settings.js file:

export default {
  name: "my-amp-site",
  bundles: ["server"],
  state: {
    //...
  },
  packages: [
    //...
  ],
};