Consider using a variable font on our website

See:

https://www.nngroup.com/articles/variable-fonts-wide-screen-layout/
Will be supported in Firefox 62 and land in Tor Browser based on Firefox 68 ESR (2019-07-09)
Other browsers: https://v-fonts.com/support/

It will allow us to have a better bold and use more font weight (for clearer heading levels for example), without having to download more fonts.

Parent Task: #15800

Original created by @sajolida on 16188 (Redmine)

To upload designs, you'll need to enable LFS and have an admin enable hashed storage. More information