Add fallback node worker for error pages

[Kaptard]

Worker would simply have endpoints for /404, /503, etc. The API would automatically redirect to the according page. If no response from fallback worker arrives (i.e. non set up or actually too busy), display original raw error instead.

[Kaptard]

Don't use any fallback worker, just write some API middleware that modifies the response object and checks for error codes. Should add an example to docs though.