Add Cloudflare Worker for serving tiles from PMTiles archives in R2

[jake-low]

Adapted from Brandon's example code here, with per-IP and per-Origin rate limiting added. I tested both rate limiting behaviors (manually lowering the rate limits so they were easier to trigger) and verified that they work.

Deployment instructions are in the README; basically npm run deploy to ship code changes.

[quincylvania]

Cool! Thanks for working on this. I think the one thing missing is a whitelist of known origins that we don't rate limit (e.g. americanamap.org, openstreetmap.us). Also, what happens if the requester doesn't set an origin?

[jake-low]

Good point re: a list of pre-approved origins; I'll work on adding that soon.

Also, what happens if the requester doesn't set an origin?

Requests that don't have an Origin header will be rate-limited together in one bucket, since if the header is not present we use a fixed string (the empty string) as the rate limit key.