Switch Java 21 CI to Bellsoft and enable update detection

Closes gh-37369

ci/scripts/detect-jdk-updates.sh

@@ -24,6 +24,10 @@ case "$JDK_VERSION" in
 		 BASE_URL="https://api.bell-sw.com/v1/liberica/releases?version-feature=20"
 		 ISSUE_TITLE="Upgrade Java 20 version in CI image"
 	;;
+	java21)
+		 BASE_URL="https://api.bell-sw.com/v1/liberica/releases?version-feature=21"
+		 ISSUE_TITLE="Upgrade Java 21 version in CI image"
+	;;
 	*)
 		echo $"Unknown java version"
 		exit 1;