session manager: open session on executor thread

This avoids blocking the main thread on startup during the http call

runelite-client/src/main/java/net/runelite/client/ClientSessionManager.java

@@ -61,6 +61,8 @@ public class ClientSessionManager
 	}
 
 	public void start()
+	{
+		executorService.execute(() ->
 		{
 			try
 			{
@@ -71,6 +73,7 @@ public class ClientSessionManager
 			{
 				log.warn("error opening session", ex);
 			}
+		});
 
 		scheduledFuture = executorService.scheduleWithFixedDelay(RunnableExceptionLogger.wrap(this::ping), 1, 10, TimeUnit.MINUTES);
 	}