Allow injection of business logic

[csharpfritz]

Introduce Action parameters on configuration that optionally allow injection of methods to be triggered before the data interaction and after the data interaction

• OnBefore delegate property added
• OnAfter delegate property added

[csharpfritz]

I'm considering closing this as it introduces more functionality that pushes towards writing more code than building a minimal API directly

[gingters]

I'd like to have these.
Idea would be to execute code after the instant API saved the changes, i.e. to send the change out to connected clients via SignalR (realtime-push about added / changed entries).