Consider using the sharp image service instead of passthroughImageService

[Greenheart]

This would improve page load time, especially on mobile networks.

I can see this was added recently. Let me know if there's another reason behind this change that I don't know about :)
https://github.com/paccao/allerthsbageri.se/blame/010054e2a1bb8a1dafcbf060232103c1b5ea331b/astro.config.js#L10

If we want to use sharp, we can remove the image: { service: passthroughImageService() } from astro.config.js. That will enable sharp which is the default image service.