Support multiple Cache properties / fields

[Dresel]

This will be necessary if users want to mix IMemoryCache and IDistributedCache (assuming implementation of #3 and #4) within one class.

Users can explicitly specify which Cache property or field (#9) should be used via the [Cache] attribute.

There might be an implicit precedence (prefer IDistributedCache over IMemoryCache and prefer properties over fields) if not specified. A warning will be emitted if multiple IDistributedCaches or multiple IMemoryCaches occur and if it is not specified explicitly which one to use.