Added preact

[eser]

Since preact doesn't support streaming renders, I hesitated to implement this one considering it's very primitive comparing to React's streaming SSR. So I wouldn't care if you close the PR without merging it.

[JoviDeCroock]

It doesn't look like the benchmark is using Suspense so I don't think streaming yes or no should make that much of a difference. That being said we did have a preliminary implementation of streaming in preact-render-to-string 😅 would love to see this land in general. According to the README there are others that don't use streaming so I do think it's fair to land this!

As this repository seems central to React (originating from the next discussion) it might be good to show that we are 2x faster and keep React as the baseline.