feat: allow providing custom cache for file loader

[getlarge]

In packages/utils, the loadExternalFile function adds request response in a memory cache (depending on node-cache package). Allow to override with custom storage, so that other cache DB (like Redis) could be used in applications.

• update function interface
• create abstract cache class
• Integrate https://github.com/mcollina/async-cache-dedupe
• wrap node-cache in abstract cache class