Apply cluster states in system context

Today cluster states are sometimes (rarely) applied in the default context
rather than system context, which means that any appliers which capture their
contexts cannot do things like remote transport actions when security is
enabled.

There are at least two ways that we end up applying the cluster state in the
default context:

1. locally applying a cluster state that indicates that the master has failed
2. the elected master times out while waiting for a response from another node

This commit ensures that cluster states are always applied in the system
context.

Mitigates elastic#53751

server/src/test/java/org/elasticsearch/cluster/coordination/NodeJoinTests.java

@@ -122,9 +122,10 @@ private static ClusterState initialState(DiscoveryNode localNode, long term, lon
     private void setupFakeMasterServiceAndCoordinator(long term, ClusterState initialState) {
         deterministicTaskQueue
             = new DeterministicTaskQueue(Settings.builder().put(Node.NODE_NAME_SETTING.getKey(), "test").build(), random());
+        final ThreadPool fakeThreadPool = deterministicTaskQueue.getThreadPool();
         FakeThreadPoolMasterService fakeMasterService = new FakeThreadPoolMasterService("test_node","test",
-            threadPool, deterministicTaskQueue::scheduleNow);
-        setupMasterServiceAndCoordinator(term, initialState, fakeMasterService, deterministicTaskQueue.getThreadPool(), Randomness.get());
+            fakeThreadPool, deterministicTaskQueue::scheduleNow);
+        setupMasterServiceAndCoordinator(term, initialState, fakeMasterService, fakeThreadPool, Randomness.get());
         fakeMasterService.setClusterStatePublisher((event, publishListener, ackListener) -> {
             coordinator.handlePublishRequest(new PublishRequest(event.state()));
             publishListener.onResponse(null);