Share data between backend and frontend

[humitos]

We've been using Cloudflare Worker to inject some data coming from the backend into the HTML that's useful/required for the frontend:

• project slug
• version slug
• resolver filename
• http response status code

In #373 (review), @agjohnson raised the idea about serializing the Response object somehow, but also mentioned that we may want to serialize a custom object at this point. Instead of using multiple meta HTML elements we could use a single script:

<script id="readthedocs-data" type="application/json">
  {
    "project": {
      "slug": "docs"
    },
    "version": {
      "slug": "latest"
    },
    "resolver": {
      "filename": "/en/latest/info.html"
    },
    "response": {
      "status": 200
    }
  }
</script>

This will give us more flexibility over time and easier to read/maintain.

[ericholscher]

This is quite similar to what we did in the old extension, as well:

https://github.com/readthedocs/readthedocs-sphinx-ext/blob/13edf78bab374f51e314e4994c319fadbab806f2/readthedocs_ext/_templates/readthedocs-insert.html.tmpl#L23