Consider adding in-memory cache

[balhoff]

Akka-HTTP provides an easy to use built-in cache: https://doc.akka.io/docs/akka-http/current/common/caching.html

Since Owlery is read-only this would work well and add parallel response capability for any queries previously performed.

@Robbie1977 @matentzn I'm using this in another server and it's working great. Any concerns about adding to Owlery?

[Robbie1977]

As long as we can access the caching settings then we can tune if any issues (unlikely).