Change the typeface used on istio.io

[craigbox]

I find our current body typeface, Barlow, a bit hard to read, at least at the weights we use it.
It also has unfixed kerning issues.

This PR experiments with changing it - I have picked Inter as a modern web-friendly option, so we can start seeing what it might look like, and consider what weights we would need to adjust.

[ilrudie]

subtle difference but I like it, TY

[Andygol]

🤞 I hope new font supports Cyrillic

[craigbox]

Does Barlow not?
Can we add another font to fall back to, for Cyrillic characters?

[Andygol]

According to https://fonts.google.com/specimen/Barlow/glyphs, Barlow has no support for scripts other than Latin. Inter (https://fonts.google.com/specimen/Inter/glyphs) supports Latin, Greek, and Cyrillic.

[craigbox]

We're already using Barlow, and you have a site in Ukrainian, which uses the Cyrillic alphabet...?

Is it using one of the fallback fonts?

[Andygol]

If you compare English version and Ukrainian, you will see differences in glyphs such as "e" (Lat) and "е" (Cyr) on the screenshots, width of letters is different and so on. And, yes, Ukrainian version use some fallback font.

istio.io	istio.io/latest/uk/

[istio-testing]

PR needs rebase.

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