eg
```
"impacts": [
            {
              "severity": 3,
              "description": "Searches might return slower than usual. Fewer redundant copies of the data exist on 2 indices [.ds-logslogslogs-2022.03.29-000001, my-index-000001].",
              "impact_areas": [ "search" ]
            }
          ]
```
server/src/test/java/org/elasticsearch/cluster/routing/allocation/ShardsAvailabilityHealthIndicatorServiceTests.java
service.calculate(true),
            equalTo(
                createExpectedResult(
                    RED,
                    "This cluster has 1 unavailable primary.",
                    Map.of("unassigned_primaries", 1),
                    List.of(
                        new HealthIndicatorImpact(1, "Cannot add data to 1 index [red-index]. Searches might return incomplete results.")
                    )
                )
            )
        );
    }
    public void testShouldBeRedWhenThereAreUnassignedPrimariesAndUnassignedReplicasOnSameIndex() {
        var clusterState = createClusterStateWith(
            List.of(index("red-index", new ShardAllocation(randomNodeId(), UNAVAILABLE), new ShardAllocation(randomNodeId(), UNAVAILABLE))),
            List.of()
        );
        var service = createAllocationHealthIndicatorService(clusterState);
        HealthIndicatorResult result = service.calculate(true);
        assertEquals(RED, result.status());
        assertEquals("This cluster has 1 unavailable primary, 1 unavailable replica.", result.summary());
        assertEquals(1, result.impacts().size());
        assertEquals(
            result.impacts().get(0),
            new HealthIndicatorImpact(1, "Cannot add data to 1 index [red-index]. Searches might return incomplete results.")
        );
    }
    public void testShouldBeRedWhenThereAreUnassignedPrimariesAndUnassignedReplicasOnDifferentIndices() {
        List<IndexMetadata> indexMetadataList = createIndexMetadataForIndexNameToPriorityMap(