Bugfix/block subscribe (#22516)

* use correct operation name

* require enable_rpc_transaction_history flag when enabling block_subscription

Co-authored-by: Zano <segfaultdoctor@protonmail.com>

validator/src/main.rs

@@ -1206,6 +1206,7 @@ pub fn main() {
         .arg(
             Arg::with_name("rpc_pubsub_enable_block_subscription")
                 .long("rpc-pubsub-enable-block-subscription")
+                .requires("enable_rpc_transaction_history")
                 .takes_value(false)
                 .help("Enable the unstable RPC PubSub `blockSubscribe` subscription"),
         )