GH-806 - Add archiving completion mode.

We now support an archiving completion mode that copies the entry to be completed into a dedicated archive to retain the completed event publications but also keep the main publication store small for more efficient data access.

Co-authored-by: Oliver Drotbohm <oliver.drotbohm@broadcom.com>

spring-modulith-events/spring-modulith-events-core/src/main/java/org/springframework/modulith/events/support/CompletionMode.java

@@ -36,7 +36,13 @@ public enum CompletionMode {
 	/**
 	 * Completes an {@link org.springframework.modulith.events.EventPublication} by removing the database entry.
 	 */
-	DELETE;
+	DELETE,
+
+	/**
+	 * Completes an {@link org.springframework.modulith.events.EventPublication} by moving the database entry to
+	 * an archive.
+	 */
+	ARCHIVE;
 
 	public static final String PROPERTY = "spring.modulith.events.completion-mode";