Access the singleton ConnectionMultiplexer or have a new IDatabase while also using IDistributedCache interface

### Is your feature request related to a problem? Please describe.
I'm trying to use our Redis server from an ASP .NET Core Web Api via the IDistributedCache interface. While this is OK, I'd also like to be able to use other data types/access modes from Redis via direct commands, i.e. I'd like to be able to use the IDatabase private member directly, preserving the IDistributedCache interface.

### Describe the solution you'd like
Some way to be able to use the same IDatabase _cached property directly or at least created a new one from a public Connect() method using the existing ConnectionMultiplexer object.

### Describe alternatives you've considered
In setup.cs, creating a singleton object RedisCache and keep a reference to it, also passing it as a service singleton instance. This may cause problems with the Connect() lock, though.

Thanks!