Define delayed event ratelimit category (#18019)

Apply ratelimiting on delayed event management separately from messages.

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---------

Co-authored-by: Andrew Morgan <1342360+anoadragon453@users.noreply.github.com>

demo/start.sh

@@ -142,6 +142,9 @@ for port in 8080 8081 8082; do
 			  per_user:
 			    per_second: 1000
 			    burst_count: 1000
+			rc_delayed_event_mgmt:
+			  per_second: 1000
+			  burst_count: 1000
 			RC
 			)
             echo "${ratelimiting}" >> "$port.config"