Add bulk SetAsync method to pre-populate cache

[noliver818]

Cache entries can only be set one item at a time

By adding an option to insert multiple items at one time, significant performance gains can be had by avoid the overhead and round-trip to a remote service. I'm thinking specifically of seeding or updating Redis in bulk. Using SetAsync in the library today is prohibitively expensive from a wall-clock perspective.

Background services would use this to seed the cache in the background for new hosts that spin up

We would deploy scheduled AWS Lambda and/or Azure Functions to insert bulk updates.