fix(gatsby): fix root resolving of resources

[wardpeet]

Description

Fixes url resolving by ignoring / queries but allow relative ones to be resolved by webpack.

Currently this doesn't load in the browser

background-image: url('./image.png');

This does when it's inside the /static folder or copied to the public folder.

background-image: url('/image.png');

With this PR both work.

I've also added a test to see that we don't regress in the future.