Cache responses

[jhamman]

This project doesn't seem to take advantage of Xpublish's cache tooling. This seems like a low-lift and something that is likely to pay pretty substantial performance dividends.

[mpiannucci]

One thing to explore here is utilizing a CDN with Cache-Control headers if cacheing on a specific request is desired. That way the server does no work if an exact request is repeated. The hard part would be somehow incorporating if the dataset had changed or updated into that strategy though.

[jhamman]

@mpiannucci -- this is a good suggestion and one that we should probably consider for other xpublish routers as well. In #45, I've tried out fastapi-cache which should provide the Cache-Control functionality out of the box (more work/testing is needed there).