Update gatsby-node.js and / or gatsby-ssr.js for server-side rendering

[selipso]

I tried to implement the example given in the new SSR features into the gatsby-node.js file but kept having issues with Authentication. It would be better to have a working example here to reference how some data can be rendered from a DynamoDB query during build-time (a query that isn't expected to change much since the data would only be updated for each new build).