Decide whether to proxy plausible.io queries, pay netlify for analytics, or do nothing.

[NunoSempere]

Plausible was being queried through a netlify snippet injection (https://app.netlify.com/sites/metaforecast/settings/deploys#post-processing), which wasn't working. I changed this to use https://github.com/4lejandrito/next-plausible in _app.tsx. But plausible recommends proxying it instead (https://plausible.io/docs/proxy/introduction). We could do that, though it sounds kind of complicated.

Instead, we could pay netlify $9/month for better analytics (e.g., because netlify serves the webpage, its analytics can't be blocked by adblockers). Personally, I think it would be worth it, but it also hurts a little bit.