Support Scylla's "shard awareness"

[whatyouhide]

From #190:

Scylla provides per-core topology information, this way the driver can send the query to the core that handles the range. It improves load balancing and reduces a shard hop. It's implemented by Python, Java, go, C++ drivers.

[peixian]

@whatyouhide I'm thinking about putting some time into adding this, since it'll be beneficial for our purposes. There's currently no ongoing effort to add this, correct?

[whatyouhide]

@peixian absolutely correct, yes! I am not too familiar with this feature really, so I’m not sure how much I'll be able to help, but I can help provide guidance around the codebase if you need to 🙃

[peixian]

I think we'd have to do this in two steps, since a prereq for the shard awareness is TokenAware LB policy in the other drives. I'll let you know if I've got questions, but I'll start taking a whack at this.