Enable failure_store feature for X-Pack full cluster restart tests (#104098)

This test suite indirectly uses functionality that requires the
failure_store functionality.

Closes #104078

x-pack/qa/full-cluster-restart/src/javaRestTest/java/org/elasticsearch/xpack/restart/AbstractXpackFullClusterRestartTestCase.java

@@ -36,6 +36,7 @@ public abstract class AbstractXpackFullClusterRestartTestCase extends Parameteri
         .keystore("xpack.watcher.encryption_key", Resource.fromClasspath("system_key"))
         .keystore("xpack.security.transport.ssl.secure_key_passphrase", "testnode")
         .feature(FeatureFlag.TIME_SERIES_MODE)
+        .feature(FeatureFlag.FAILURE_STORE_ENABLED)
         .build();
 
     public AbstractXpackFullClusterRestartTestCase(FullClusterRestartUpgradeStatus upgradeStatus) {