Bump FLEET_AGENTS_MAPPINGS_VERSION so the new mapping applies on upgrades (elastic#134957)

Author: michel-laterman

x-pack/plugin/fleet/src/main/java/org/elasticsearch/xpack/fleet/Fleet.java

@@ -79,7 +79,7 @@ public class Fleet extends Plugin implements SystemIndexPlugin {
     private static final String MAPPING_VERSION_VARIABLE = "fleet.version";
     private static final List<String> ALLOWED_PRODUCTS = List.of("kibana", "fleet");
     private static final int FLEET_ACTIONS_MAPPINGS_VERSION = 2;
-    private static final int FLEET_AGENTS_MAPPINGS_VERSION = 4;
+    private static final int FLEET_AGENTS_MAPPINGS_VERSION = 5;
     private static final int FLEET_ENROLLMENT_API_KEYS_MAPPINGS_VERSION = 3;
     private static final int FLEET_SECRETS_MAPPINGS_VERSION = 1;
     private static final int FLEET_POLICIES_MAPPINGS_VERSION = 2;