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
assertThat(
            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 [restarting-index]. Searches might return incomplete results."
                        )
                    )
                )
            )
        );
    }
    private HealthIndicatorResult createExpectedResult(
        HealthStatus status,
        String summary,
        Map<String, Object> details,
        List<HealthIndicatorImpact> impacts
    ) {
        return new HealthIndicatorResult(NAME, DATA, status, summary, new SimpleHealthIndicatorDetails(addDefaults(details)), impacts);
    }
    private static List<IndexMetadata> createIndexMetadataForIndexNameToPriorityMap(Map<String, Integer> indexNameToPriorityMap) {
        List<IndexMetadata> indexMetadataList = new ArrayList<>();
        if (indexNameToPriorityMap != null) {
            for (Map.Entry<String, Integer> indexNameToPriority : indexNameToPriorityMap.entrySet()) {
                String indexName = indexNameToPriority.getKey();