Inactive replica of new primary shard is green (elastic#99995)

When we have a new initialisation of a primary shard we consider the
this indicator `green` based on the idea that this are unexceptional
events in the cluster's lifecycle. However, when we have a replica of
this shard that is inactive we turn to `yellow`. 

With this PR, we change this behaviour to signal that if the primary is
inactive and that is `green`, then an inactive replica of this shard is
also `green`.

Fixes elastic#99951

docs/changelog/99995.yaml

@@ -0,0 +1,6 @@
+pr: 99995
+summary: When a primary is inactive but this is considered expected, the same applies for the replica of this shard.
+area: Health
+type: enhancement
+issues:
+ - 99951

server/src/main/java/org/elasticsearch/cluster/routing/allocation/ShardsAvailabilityHealthIndicatorService.java

@@ -402,7 +402,7 @@ private class ShardAllocationCounts {
         private final Map<Diagnosis.Definition, Set<String>> diagnosisDefinitions = new HashMap<>();
 
         public void increment(ShardRouting routing, ClusterState state, NodesShutdownMetadata shutdowns, boolean verbose) {
-            boolean isNew = isUnassignedDueToNewInitialization(routing);
+            boolean isNew = isUnassignedDueToNewInitialization(routing, state);
             boolean isRestarting = isUnassignedDueToTimelyRestart(routing, shutdowns);
             available &= routing.active() || isRestarting || isNew;
             if ((routing.active() || isRestarting || isNew) == false) {
@@ -454,8 +454,14 @@ private static boolean isUnassignedDueToTimelyRestart(ShardRouting routing, Node
         return now - restartingAllocationDelayExpiration <= 0;
     }
 
-    private static boolean isUnassignedDueToNewInitialization(ShardRouting routing) {
-        return routing.primary() && routing.active() == false && getInactivePrimaryHealth(routing) == ClusterHealthStatus.YELLOW;
+    private static boolean isUnassignedDueToNewInitialization(ShardRouting routing, ClusterState state) {
+        if (routing.active()) {
+            return false;
+        }
+        // If the primary is inactive for unexceptional events in the cluster lifecycle, both the primary and the
+        // replica are considered new initializations.
+        ShardRouting primary = routing.primary() ? routing : state.routingTable().shardRoutingTable(routing.shardId()).primaryShard();
+        return primary.active() == false && getInactivePrimaryHealth(primary) == ClusterHealthStatus.YELLOW;
     }
 
     /**
@@ -815,13 +821,15 @@ public String getSymptom() {
                 || primaries.unassigned_new > 0
                 || primaries.unassigned_restarting > 0
                 || replicas.unassigned > 0
+                || replicas.unassigned_new > 0
                 || replicas.unassigned_restarting > 0
                 || primaries.initializing > 0
                 || replicas.initializing > 0) {
                 builder.append(
                     Stream.of(
                         createMessage(primaries.unassigned, "unavailable primary shard", "unavailable primary shards"),
                         createMessage(primaries.unassigned_new, "creating primary shard", "creating primary shards"),
+                        createMessage(replicas.unassigned_new, "creating replica shard", "creating replica shards"),
                         createMessage(primaries.unassigned_restarting, "restarting primary shard", "restarting primary shards"),
                         createMessage(replicas.unassigned, "unavailable replica shard", "unavailable replica shards"),
                         createMessage(primaries.initializing, "initializing primary shard", "initializing primary shards"),
@@ -861,6 +869,8 @@ public HealthIndicatorDetails getDetails(boolean verbose) {
                         replicas.unassigned,
                         "initializing_replicas",
                         replicas.initializing,
+                        "creating_replicas",
+                        replicas.unassigned_new,
                         "restarting_replicas",
                         replicas.unassigned_restarting,
                         "started_replicas",

server/src/test/java/org/elasticsearch/cluster/routing/allocation/ShardsAvailabilityHealthIndicatorServiceTests.java

@@ -533,17 +533,20 @@ public void testShouldBeYellowWhenRestartingReplicasReachedAllocationDelay() {
         );
     }
 
-    public void testShouldBeGreenWhenThereAreInitializingPrimaries() {
-        var clusterState = createClusterStateWith(List.of(index("restarting-index", new ShardAllocation("node-0", CREATING))), List.of());
+    public void testShouldBeGreenWhenThereAreInitializingPrimariesAndReplicas() {
+        var clusterState = createClusterStateWith(
+            List.of(index("restarting-index", new ShardAllocation("node-0", CREATING), new ShardAllocation("node-1", CREATING))),
+            List.of()
+        );
         var service = createShardsAvailabilityIndicatorService(clusterState);
 
         assertThat(
             service.calculate(true, HealthInfo.EMPTY_HEALTH_INFO),
             equalTo(
                 createExpectedResult(
                     GREEN,
-                    "This cluster has 1 creating primary shard.",
-                    Map.of("creating_primaries", 1),
+                    "This cluster has 1 creating primary shard, 1 creating replica shard.",
+                    Map.of("creating_primaries", 1, "creating_replicas", 1),
                     emptyList(),
                     emptyList()
                 )
@@ -1765,6 +1768,8 @@ private static Map<String, Object> addDefaults(Map<String, Object> override) {
             override.getOrDefault("started_primaries", 0),
             "unassigned_replicas",
             override.getOrDefault("unassigned_replicas", 0),
+            "creating_replicas",
+            override.getOrDefault("creating_replicas", 0),
             "initializing_replicas",
             override.getOrDefault("initializing_replicas", 0),
             "restarting_replicas",