defaultconf: set max_known_events default as 1000

Signed-off-by: Yonle <yonle@lecturify.net>

config.js.example

@@ -67,7 +67,7 @@ module.exports = {
   //
   // Setting as 0 will store known events to memory without limit until the subscription is closed.
   // Reduce this value if memory usage is high. But don't go too low as duplicates will be forwarded to client.
-  max_known_events: 5000,
+  max_known_events: 1000,
 
   // Wait for every connected relays send EOSE.
   // Could improve accuracy on received events.