feat: enable basic rate limiting

[djdembeck]

Recent investigations from #479 performance issues caused me to find there is room for abuse of the public service:

• Enabling Cloudflare bot fight mode, would overzealously block Plex agents.
• There were tons of retries of invalid asins that matched the asin regex (and thus proceeded to try the request).
• A user could send as many requests as they wanted and Cloudlfare may not rate limit or block them.

This PR aims to address these issues by doing the following:

• Correctly process incoming IPs in a docker container (by trusting upstream proxy).
• Rate limit ALL routes if there are >100 requests within a minute by default. Allow adjusting this via environment var MAX_REQUESTS.
• Update the ASIN regex to be stricter, requiring it either stars with B (as a large number of early books use), or it is fully numeric (as all new books are).
• Enable Redis on the public server.

Eventually rate limit repeated 404 or 400 attempts of different URLs, when this is resolved: fastify/fastify-rate-limit#260

[github-actions]

Coverage report

St.❔	Category	Percentage	Covered / Total
🟢	Statements	100%	805/805
🟢	Branches	100%	258/258
🟢	Functions	100%	157/157
🟢	Lines	100%	759/759

Test suite run success

227 tests passing in 21 suites.

Report generated by 🧪jest coverage report action from 12955e5