Consider refactoring existing annotations

[tombentley]

Right now we have @Kraft, @ZooKeeper and @BrokerCluster, but there's an alternative formulation that might work out cleaner:

@interface MetadataQuorum {
    QuorumType type() default COMBINED;
    int size() default 1;
}
enum QuorumType {
    @Deprecated ZK, // use ZK
    COMBINED, // use combined node (broker+controllers)
    DEDICATED // use dedicated controllers
}
@interface Brokers {
    int value() default 1;
}

This feels like a cleaner separation where there's a single annotation for specifying the details for the controller quorum and a separate annotation for the broker cluster. It would require the backend code to figure out (or reject) interesting combinations like @MetadataQuorum(size=3) @Brokers(1) (which given the default quorum type is COMBINED is a contradiction).