### Elasticsearch Version

8.4, 8.5, 8.6

### Installed Plugins

_No response_

### Java Version

_bundled_

### OS Version

Darwin

### Problem Description

The shards availability indicator should always be reporting diagnosis when its status is RED/YELLOW.
However, when an index is on a data node that runs out of disk space it will report RED but no diagnosis.

### Steps to Reproduce

Have multi-node cluster where a data (non-master) node that hosts an index runs out of disk space (the index cannot relocate somewhere else).
Call the Health API and the output will be something along these lines:
```
    "shards_availability": {
      "status": "red",
      "symptom": "This cluster has all shards available.",
      "details": {
        "initializing_primaries": 1,
        "started_replicas": 0,
        "initializing_replicas": 0,
        "unassigned_primaries": 0,
        "started_primaries": 1,
        "creating_primaries": 0,
        "unassigned_replicas": 0,
        "restarting_primaries": 0,
        "restarting_replicas": 0
      },
      "impacts": [
        {
          "id": "elasticsearch:health:shards_availability:impact:primary_unassigned",
          "severity": 1,
          "description": "Cannot add data to 1 index [test_index]. Searches might return incomplete results.",
          "impact_areas": [
            "ingest",
            "search"
          ]
        }
      ] 
    }
``` 

### Logs (if relevant)

_No response_
server/src/test/java/org/elasticsearch/cluster/routing/allocation/ShardsAvailabilityHealthIndicatorServiceTests.java
) {
        return createAllocationHealthIndicatorService(Settings.EMPTY, clusterState, decisions, new SystemIndices(List.of()));
    }
    private static ShardsAvailabilityHealthIndicatorService createShardsAvailabilityIndicatorService(
        Settings nodeSettings,
        ClusterState clusterState,
        final Map<ShardRoutingKey, ShardAllocationDecision> decisions
    ) {
        return createAllocationHealthIndicatorService(nodeSettings, clusterState, decisions, new SystemIndices(List.of()));
    }
    private static ShardsAvailabilityHealthIndicatorService createAllocationHealthIndicatorService(
        Settings nodeSettings,
        ClusterState clusterState,
        final Map<ShardRoutingKey, ShardAllocationDecision> decisions,
        SystemIndices systemIndices
    ) {
        var clusterService = mock(ClusterService.class);
        when(clusterService.state()).thenReturn(clusterState);
        var clusterSettings = new ClusterSettings(nodeSettings, ClusterSettings.BUILT_IN_CLUSTER_SETTINGS);
        when(clusterService.getClusterSettings()).thenReturn(clusterSettings);
        var allocationService = mock(AllocationService.class);
        when(allocationService.explainShardAllocation(any(), any())).thenAnswer((Answer<ShardAllocationDecision>) invocation -> {
            ShardRouting shardRouting = invocation.getArgument(0);
            var key = new ShardRoutingKey(shardRouting.getIndexName(), shardRouting.getId(), shardRouting.primary());
            return decisions.getOrDefault(key, ShardAllocationDecision.NOT_TAKEN);
        });
        return new ShardsAvailabilityHealthIndicatorService(clusterService, allocationService, systemIndices);
    }
}