Linked key expiration triggers.

#15

Linked expiration works for:
Triggers
Absolute expiration

But not for:
Sliding expiration
Manual removal
Memory pressure removal
FYI: This pattern is already in use for IServiceProvider.
https://github.com/aspnet/KRuntime/blob/eb94c849080d63f31b4a423eae76c339da1a557e/src/klr.host/ServiceProviderLocator.cs