Nix cache proxy for R2

Heavily based on https://github.com/piperswe/nix-cache

Create an A record on the subdomain you want this Worker to run on which points to 192.0.2.1 (see https://community.cloudflare.com/t/a-record-name-for-worker/98841/2 for why)
Edit wrangler.toml
- account_id should be your Cloudflare account's tag
- route should be the subdomain this Worker will run on followed by /*
- bucket_name and preview_bucket_name should be the name of the R2 bucket you'll use
Run npm run login to login to Wrangler
Run npm run deploy!
Upload an index.html to your bucket if you want a landing page