v14: Async Cache Refreshers

[mattbrailsford]

Which Umbraco version are you using? (Please write the exact version, example: 10.1.0)

v14

Bug summary

The current cache refreshers implementation is synchronous only and so doesn't allow executing async code to respond to cache changes.

Specifics

In Umbraco Commerce v15 our who API has been made async and so we need to be able to execute our async services in response to a cache refresh notification.

Steps to reproduce

n/a

Expected result / actual result

I expect to be able to execute async code in response to a cache refresh notification