Driver extensions for tablet awareness

[bhalevy]

This is an umbrella issue for extending the driver for tablets.
Derived from Tablets implementation plan

[bhalevy]

@scylladb/cpp-driver-maint please add to Tablets project (and tablets label would be nice too).
I don't have the perms to do that in this reposoitory.

@BorishuV please change my permissions to be able to edit projects and labels.