Add vote account address to vote subscription

(cherry picked from commit 331b953551)

# Conflicts:
#	core/src/cluster_info_vote_listener.rs
#	rpc/src/rpc_pubsub.rs
#	rpc/src/rpc_subscriptions.rs

client/src/rpc_response.rs

@@ -290,6 +290,8 @@ pub struct RpcIdentity {
 #[derive(Serialize, Deserialize, Clone, Debug)]
 #[serde(rename_all = "camelCase")]
 pub struct RpcVote {
+    /// Vote account address, as base-58 encoded string
+    pub vote_pubkey: String,
     pub slots: Vec<Slot>,
     pub hash: String,
     pub timestamp: Option<UnixTimestamp>,