Batching statement authorization improvements

[ivansenic]

Currently when using CQL or gRPC APIs and sending batch statements, each statement in that batch is being authorized in StargateQueryHandler. Meaning if I have 100 insert statements that target same table, we would would do 100 authorizations. Depending on the authorization type this can represent significant overhead,

We can optimize this in a way that we collect set of authorizations needed for a batch statement. These should be distinguished by the needed authz scope (depending on the statement type) and target keyspace & table. Once we extract those, we only execute minimal amount of authorizations.

We can also use this ticket to actually create a StatementAuthorizer class and extract the logic from the query handler. Furthermore, we could see how to correctly abstract this so that it can be shared between all persistence modules.