Add HTML pre-rendering

[FKolwa]

Replace dr:surge with react-spa-prerender
Add react-spa config
Add new postbuild step

What hat changed?
To increase SEO performance for our front-end I have added a postbuild step which will generate static pre-rendered HTML files from our static Javascript page.

It will turn this:

  <script defer="defer" src="/main.bundle.js"></script>
  <link href="/main.css" rel="stylesheet">

Into this:

<div id="root">
    <div class="pf-c-page pf-m-resize-observer pf-m-breakpoint-md pf-m-height-breakpoint-2xl"><a
        class="pf-c-button pf-m-primary pf-c-skip-to-content" href="#primary-app-container">Skip to Content</a>
      ...

New Output

Closes: #90

[major]

Nice find!