Choose more appropriate options for pubsub websocket server (#8354)

* Choose more sensible options for pubsub websocket server

* Increase max payload size for pubsub service

core/src/rpc_pubsub_service.rs

@@ -37,6 +37,8 @@ impl PubSubService {
                         });
                         session
                 })
+                .max_connections(1000) // Arbitrary, default of 100 is too low
+                .max_payload(10 * 1024 * 1024 + 1024) // max account size (10MB) + extra (1K)
                 .start(&pubsub_addr);
 
                 if let Err(e) = server {