do some webp conversion, to reduce loading times

[alicewriteswrongs]

Pre-Flight checklist

• [x] Screenshots and design review for any changes that affect layout or styling
  • [x] Desktop screenshots
  • [x] Mobile width screenshots
  • [x] Tag @ferdi or @pdpinch for review
• [x] Testing
  • [x] Code is tested
  • [x] Changes have been manually tested

What are the relevant tickets?

closes #97

What's this PR do?

converts a bunch of key images over to webp format from png or jpeg.

How should this be manually tested?

the site should look normal and the same as on the main branch. I don't think I messed anything up when converting images, but it's certainly possible and so good to test!

screens:

[github-actions[bot]]

🚀 Deployed on https://ocw-www-pr-98--ocw-next.netlify.app

[github-actions[bot]]

Lighthouse results:

results for https://ocw-www-pr-98--ocw-next.netlify.app/:

Accessibility	Best Practices	Performance	Progressive Web App	SEO
72 🙂	80 😄	34 😰	42 😨	62 😐

results for https://ocw-www-pr-98--ocw-next.netlify.app/search/:

Accessibility	Best Practices	Performance	Progressive Web App	SEO
71 🙂	93 🎉	78 🙂	42 😨	55 😟

[gumaerc]

I'm not sure exactly what the cause would be, but this seems to have actually decreased performance on the home page? This is a screenshot of a lighthouse run from the most recent PR merged here:

[gumaerc]

For what it's worth, this is what I get running lighthouse in an incognito window locally: