Introduce an SSR mode for Greenwood

[thescientist13]

Type of Change

• New Feature Request
• Documentation / Website
• Improvement / Suggestion
• Bug
• Other (please clarify below)

Summary

As part of ongoing discovery in #576 , one the key action items needed is to enable a true SSR mode that will allow running Greenwood as a process on a server such that at least for the serve command, will effectively just run the koa server to generate pages / templates on the fly but serving bundled rollup code.

Details

Basically we need to add ssr as a mode such when a user runs npm run serve, we build and bundle all the pages and assets like normal, but additionally keep the Koa server going to keep serving requests to pages and content but in a built / production context.

We might also want to rename the current serve command to a demo since now server will require a special set of expectations on its own that should be specifically find tuned for running on a server as a process.

Thoughts / questions

1. Server side rendering support for local development?
2. Still need to explore a bit more how server side templating and data fetching would work
3. Now that we need Koa for more than a dev server, should explore using something like fastify?
4. Should we persist puppeteer in this scenario? Making this something like an optionalDependency would be amazing and only install it on demand when needed / detected
5. Should we think about re-branding Greenwood at this point, since it won't just be an SSG anymore?