### Description

**Description**

We have been conducting user research on the copy and other aspects of the health API and have a few concrete copy suggestions from the user interviews. 

**StableMasterHealthIndicator**

1. We have user action `UNSTABLE_MASTER_DEPLOYMENT_MANAGEMENT_IMPACT` ([line](https://github.com/elastic/elasticsearch/blob/master/server/src/main/java/org/elasticsearch/cluster/coordination/StableMasterHealthIndicatorService.java#L62). I propose

_Before_: "Scheduled tasks such as Watcher, ILM, and SLM will not work. The _cat APIs will not work." 

_After_:  "Scheduled tasks such as Watcher, Index Lifecycle Management and Snapshot Lifecycle Management will not ...."  instead of using the abbreviations. Some users might not know the terms but at least this gives them more to search on and learn from. 

2. The `UNSTABLE_MASTER_BACKUP_IMPACT` ([line](https://github.com/elastic/elasticsearch/blob/100f5acd345dd13d8c8d17b93392d4b217bc50a2/server/src/main/java/org/elasticsearch/cluster/coordination/StableMasterHealthIndicatorService.java#L64)), I propose making the impact even clearer in laymen terms. 

_Before_: "Snapshot and restore will not work. Searchable snapshots cannot be mounted."
_After_: "Snapshot and restore will not work, your data will not be backed up. Searchable snapshots cannot be mounted, search on backup data will not return results."

I propose we do the same for the messages in the `SlmHealthIndicatorService`, and use the unabbreviated messages where shown to users. 
server/src/test/java/org/elasticsearch/cluster/routing/allocation/ShardsAvailabilityHealthIndicatorServiceTests.java
)
            ),
            List.of()
        );
        var service = createAllocationHealthIndicatorService(clusterState);
        assertThat(
            service.calculate(true, HealthInfo.EMPTY_HEALTH_INFO),
            equalTo(
                createExpectedResult(
                    YELLOW,
                    unavailableReplicas.size() > 1
                        ? "This cluster has " + unavailableReplicas.size() + " unavailable replicas."
                        : "This cluster has 1 unavailable replica.",
                    Map.of(
                        "started_primaries",
                        1,
                        "unassigned_replicas",
                        unavailableReplicas.size(),
                        "started_replicas",
                        availableReplicas.size()
                    ),
                    List.of(
                        new HealthIndicatorImpact(
                            NAME,
                            ShardsAvailabilityHealthIndicatorService.REPLICA_UNASSIGNED_IMPACT_ID,
                            2,
                            "Searches might be slower than usual. Fewer redundant copies of the data exist on 1 index [yellow-index].",
                            List.of(ImpactArea.SEARCH)
                        )
                    ),