gatsby-plugin-preload-fonts - custom cache path

[giladsegal]

gatsby-plugin-preload-fonts generates a cache file with a hardcoded name font-preload-cache.json. I want to make that file path configurable.

That's my use-case: During the build process, I use environment variables, to generate two different versions of my website. All versions share common pages, but each version has a few unique pages. Currently, I can't set the path of font-preload-cache.json per website version so the plugin can only work with a single version of my website. To get around it I created the json files for both versions and merged them manually.

This can be solved by:

1. Passing the custom cache location to the gatsby-preload-fonts script
2. Passing the custom cache location to the gatsby-plugin-preload-fonts configuration in ./gatsby-config.js

P.S
I can also contribute the code if you agree it has value.