Disable the PubSub vote subscription by default (#13600)

The --rpc-pubsub-enable-vote-subscription flag may be used to enable it.
The current vote subscription is problematic because it emits a
notification for *every* vote, so hundreds a second in a real cluster.
Critically it's also missing information about *who* is voting,
rendering all those notifications practically useless.

Until these two issues can be resolved, the vote subscription is not
much more than a potential DoS vector.

(cherry picked from commit 5d72e52ad0)

Co-authored-by: Michael Vines <mvines@gmail.com>

validator/src/main.rs

@@ -1252,6 +1252,12 @@ pub fn main() {
                 .validator(solana_net_utils::is_host)
                 .help("IP address to bind the RPC port [default: use --bind-address]"),
         )
+        .arg(
+            Arg::with_name("rpc_pubsub_enable_vote_subscription")
+                .long("rpc-pubsub-enable-vote-subscription")
+                .takes_value(false)
+                .help("Enable the unstable RPC PubSub `voteSubscribe` subscription"),
+        )
         .arg(
             Arg::with_name("rpc_pubsub_max_connections")
                 .long("rpc-pubsub-max-connections")
@@ -1457,6 +1463,7 @@ pub fn main() {
             )
         }),
         pubsub_config: PubSubConfig {
+            enable_vote_subscription: matches.is_present("rpc_pubsub_enable_vote_subscription"),
             max_connections: value_t_or_exit!(matches, "rpc_pubsub_max_connections", usize),
             max_fragment_size: value_t_or_exit!(matches, "rpc_pubsub_max_fragment_size", usize),
             max_in_buffer_capacity: value_t_or_exit!(