Switch baked images to PNG instead of webp

[ikesau]

WebP supported puttered out across all OS's and so despite smaller filesizes, it's impacting the shareability of our inline images.

We should bake the images as PNG instead.

owid-grapher/baker/GDriveImagesBaker.tsx

Lines 89 to 94 in f8f12b1

	return sharp(buffer)
	.resize(width)
	.webp({
	lossless: true,
	})
	.toFile(localResizedFilepath)

And make sure any place that's assuming webp is changed to PNG instead.