Use filename.hash.ext for production static assets

[synap5e]

When the css/json files are changed, they do not update in for users due to the multiple-day cache times.

To fix, assets should be versioned by their hash.
This could be implemented by extending url_for to read asset hashes from a json, and modify the filename if the file exists and has an entry for the requested url.
When built, the json could be generated .

[gabbyprecious]

Hello, Is anyone assigned to it, can I jump on it?

[synap5e]

Probably best if I take this one; it will require messing with the build system which only I have access to. The repo is mirrored on gitlab and uses their pipeline system for builds.

Thanks for the offer though :) Some of the other issues here might make more sense to pick up, I'll go through and make sure the tags are updated and assign myself to a few that I plan to take.