Add solution for rate limits

[rosszurowski]

Airtable mentions in the docs that it limits API calls:

The API is limited to 5 requests per second. If you exceed this rate, you will receive a 429 status code and will need to wait 30 seconds before subsequent requests will succeed.

If you need a higher request rate, they suggest either using retry logic or a caching proxy.

I think it'd be easy enough to add a caching layer, especially seeing simple implementations like the micro-open-graph use of memory-cache. Maybe just cache results for 30 seconds by default, configurable via env variable?