Make hash for fetch.js optional

[coder-hugo]

Summary

If you do not use the fetch functionality it would be nice if you could prevent gridsome from rendering the hash to each and every page.

Basic example

Motivation

I'm trying to optimize the deployment of our gridsome app. With the default configuration the content of each and every page changes with every build although the page data is identical. To fix this I adapted the webpack configuration of our project to use stable hashes in the asset filenames. But the content of the pages still changes as the hash for the fetch.js is different for every build. This means we have to upload each and every page again although just a few of them really have changed. The output of our project has some hundreds of mega bytes so the deployment takes unnecessary long due to the changing hash in each and every page.