### 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/cluster/coordination/StableMasterHealthIndicatorService.java
/**
     * Returns the name of the node with the given nodeId, as seen in the cluster state at this moment. The name of a node is optional,
     * so if the node does not have a name (or the node with the given nodeId is no longer in the cluster state), null is returned.
     * @param nodeId The id of the node whose name is to be returned
     * @return The current name of the node, or null if the node is not in the cluster state or does not have a name
     */
    @Nullable
    private String getNameForNodeId(String nodeId) {
        DiscoveryNode node = clusterService.state().nodes().get(nodeId);
        if (node == null) {
            return null;
        } else {
            String nodeName = node.getName();
            return Objects.requireNonNullElse(nodeName, null);
        }
    }
    /**
     * This method returns the only user action that is relevant when the master is unstable -- contact support.
     * @param explain If true, the returned list includes a UserAction to contact support, otherwise an empty list
     * @return a single UserAction instructing users to contact support.
     */
    private List<Diagnosis> getContactSupportUserActions(boolean explain) {
        if (explain) {
            return List.of(CONTACT_SUPPORT_USER_ACTION);
        } else {
            return List.of();
        }
    }
}