Add New Guardian Headline Font Weight: Regular

Add the "Regular" font weight (400) of the Guardian Headline font to dotcom for articles, and possibly to apps and Editions.
```[tasklist]
### Tasks
- [ ] Investigate whether the new font files work with the Android interceptor mechanism
- [ ] Add the new font files to the iOS pre-warmed assets file
- [ ] Add the new `font-face` declarations to DCAR
- [ ] Possibly include `ttf` versions of these font files in the apps bundles
- [ ] Test the impact of these changes with CWVs (AB test?)
- [ ] Revisit our font loading mechanism with Ravi
```