Refresh: Add final gallery images #15307

[stephaniehobson]

One-line summary

Add final gallery images #15307

Significant changes and points to review

• Images sizes were chosen to address:
  • highest possible request size in high res
  • highest likely request size in both high and low res
  • lowest likely request size (lower is always possible)
  • if there was a large file size gap between those sizes likely middle sizes were picked
  • I honestly don't know what the right decision is here and I can share my spreadsheet if you like but I'd mostly prefer not to have to think about this again for a few weeks.
• everything below 1440px sizing was calculated without taking gutters into account, since the sizes media query does not take gutters into account
  • we can't pass CSS variables to sizes so it starts to be come unmanageable to consider gutters (they're only 16px wide so it's not a big performance hit)
• all images should be .jpg and optimized
• alt text is not final so I did not wrap it for l10n
  • it's important to get feedback on what we have
  • we can make the display conditional on translation once we have them

Issue / Bugzilla link

#15307

Testing

Test at 1920, 1440, 1366, 1280, 1024, 768, 640, 360.
Test in both high and low res.