Support for keyspace notifications

### Feature request type

enhancement

### Is your feature request related to a problem? Please describe

Keyspace notifications allow clients to subscribe to Pub/Sub channels in order to receive events affecting the Garnet data set in some way.

### Describe the solution you'd like

We already have PubSub support, but it is only for user defined channels.
It will be nice to support keyspace notification as described [here](https://redis.io/docs/latest/develop/use/keyspace-notifications/).

### Describe alternatives you've considered

N/A

### Additional context

_No response_

Start by reading the Redis keyspace notification documentation linked in the issue and tracing Garnet's existing Pub/Sub support. Compare the requested notification behavior with the current user-defined channel behavior. Done means Redis clients can subscribe to the relevant keyspace notification channels and receive events affecting the Garnet data set.

Written by the indexing model from the issue text.