### 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/main/java/org/elasticsearch/health/node/DiskHealthIndicatorService.java
import java.util.Collection;
import java.util.Collections;
import java.util.HashMap;
import java.util.HashSet;
import java.util.List;
import java.util.Locale;
import java.util.Map;
import java.util.Objects;
import java.util.Set;
import java.util.stream.Collectors;
import java.util.stream.Stream;
import static org.elasticsearch.cluster.node.DiscoveryNode.DISCOVERY_NODE_COMPARATOR;
import static org.elasticsearch.health.node.HealthIndicatorDisplayValues.are;
import static org.elasticsearch.health.node.HealthIndicatorDisplayValues.getSortedUniqueValuesString;
import static org.elasticsearch.health.node.HealthIndicatorDisplayValues.getTruncatedIndices;
import static org.elasticsearch.health.node.HealthIndicatorDisplayValues.indices;
import static org.elasticsearch.health.node.HealthIndicatorDisplayValues.indicesComparatorByPriorityAndName;
import static org.elasticsearch.health.node.HealthIndicatorDisplayValues.regularNoun;
import static org.elasticsearch.health.node.HealthIndicatorDisplayValues.regularVerb;
import static org.elasticsearch.health.node.HealthIndicatorDisplayValues.these;
/**
 * This indicator reports the clusters' disk health aka if the cluster has enough available space to function.
 * Indicator will report YELLOW status when:
 * - a data node's disk usage is above the high watermark and it's not relocating any of its shards.
 * - a non data node's disk usage is above the high watermark.
 * Indicator will report RED status when:
 * - an index has the INDEX_READ_ONLY_ALLOW_DELETE_BLOCK which indicates that an index has been blocked because a node was out of space.
 * - any node's disk usage is above the flood stage watermark.
 */
public class DiskHealthIndicatorService implements HealthIndicatorService {