Improve transient settings deprecation message (elastic#79504)

Update message as per docs team's suggestion.

Author: grcevski

x-pack/plugin/deprecation/src/main/java/org/elasticsearch/xpack/deprecation/ClusterDeprecationChecks.java

@@ -14,9 +14,9 @@ public class ClusterDeprecationChecks {
     static DeprecationIssue checkTransientSettingsExistence(ClusterState state) {
         if (state.metadata().transientSettings().isEmpty() == false) {
             return new DeprecationIssue(DeprecationIssue.Level.WARNING,
-                "Transient cluster settings are in the process of being removed.",
+                "Transient cluster settings are deprecated",
                 "https://ela.st/es-deprecation-7-transient-cluster-settings",
-                "Use persistent settings to define your cluster settings instead.",
+                "Use persistent settings to configure your cluster.",
                 false,
                 null);
         }

x-pack/plugin/deprecation/src/test/java/org/elasticsearch/xpack/deprecation/ClusterDeprecationChecksTests.java

@@ -18,24 +18,31 @@
 public class ClusterDeprecationChecksTests extends ESTestCase {
 
     public void testCheckTransientSettingsExistence() {
+        Settings persistentSettings = Settings.builder()
+            .put("xpack.monitoring.collection.enabled", true)
+            .build();
+
         Settings transientSettings = Settings.builder()
             .put("indices.recovery.max_bytes_per_sec", "20mb")
+            .put("action.auto_create_index", true)
+            .put("cluster.routing.allocation.enable", "primaries")
             .build();
         Metadata metadataWithTransientSettings = Metadata.builder()
+            .persistentSettings(persistentSettings)
             .transientSettings(transientSettings)
             .build();
 
         ClusterState badState = ClusterState.builder(new ClusterName("test")).metadata(metadataWithTransientSettings).build();
         DeprecationIssue issue = ClusterDeprecationChecks.checkTransientSettingsExistence(badState);
         assertThat(issue, equalTo(
             new DeprecationIssue(DeprecationIssue.Level.WARNING,
-                "Transient cluster settings are in the process of being removed.",
+                "Transient cluster settings are deprecated",
                 "https://ela.st/es-deprecation-7-transient-cluster-settings",
-                "Use persistent settings to define your cluster settings instead.",
+                "Use persistent settings to configure your cluster.",
                 false, null)
         ));
 
-        Settings persistentSettings = Settings.builder()
+        persistentSettings = Settings.builder()
             .put("indices.recovery.max_bytes_per_sec", "20mb")
             .build();
         Metadata metadataWithoutTransientSettings = Metadata.builder()