[BAEL-4768] Snapshotting the Aggregate in Axon (#11103)

* Add configuration class

Add configuration class

#BAEL-4768

* Add SnapshotTriggerDefinition bean creation method

Add SnapshotTriggerDefinition bean creation method

#BAEL-4768

* Add SnapshotTriggerDefinition bean name

Add SnapshotTriggerDefinition bean name

#BAEL-4768

* Add threshold behind property value

Add threshold behind property value. Default to 250.

#BAEL-4768

* Add link to the readme

Add a link to the article in the readme

#BAEL-4768

* Process review comments

- Drop readme line
- Adjust parameter indentation of config class

#BAEL-4768

axon/src/main/java/com/baeldung/axon/OrderApplicationConfiguration.java

@@ -0,0 +1,18 @@
+package com.baeldung.axon;
+
+import org.axonframework.eventsourcing.EventCountSnapshotTriggerDefinition;
+import org.axonframework.eventsourcing.SnapshotTriggerDefinition;
+import org.axonframework.eventsourcing.Snapshotter;
+import org.springframework.beans.factory.annotation.Value;
+import org.springframework.context.annotation.Bean;
+import org.springframework.context.annotation.Configuration;
+
+@Configuration
+public class OrderApplicationConfiguration {
+
+    @Bean
+    public SnapshotTriggerDefinition orderAggregateSnapshotTriggerDefinition(Snapshotter snapshotter,
+                                                                             @Value("${axon.aggregate.order.snapshot-threshold:250}") int threshold) {
+        return new EventCountSnapshotTriggerDefinition(snapshotter, threshold);
+    }
+}

axon/src/main/java/com/baeldung/axon/commandmodel/order/OrderAggregate.java

@@ -23,7 +23,7 @@ import java.util.Map;
 
 import static org.axonframework.modelling.command.AggregateLifecycle.apply;
 
-@Aggregate
+@Aggregate(snapshotTriggerDefinition = "orderAggregateSnapshotTriggerDefinition")
 public class OrderAggregate {
 
     @AggregateIdentifier