Report full stack trace for non-state file settings transforms (elast…

…ic#101346)

In most cases file based settings apply transformations from
configuration to cluster state. However, there exists "non state"
transformations as well. When these are run, any errors are stored in
cluster state. This commit fixes a bug in handling of these exception
cases where just the exception messages, instead of the full stack
trace, was captured.

docs/changelog/101346.yaml

@@ -0,0 +1,5 @@
+pr: 101346
+summary: Report full stack trace for non-state file settings transforms
+area: Infra/Settings
+type: bug
+issues: []

server/src/main/java/org/elasticsearch/reservedstate/service/ReservedClusterStateService.java

@@ -239,7 +239,7 @@ public void onFailure(Exception e) {
             @Override
             public void onFailure(Exception e) {
                 // If we encounter an error while runnin the non-state transforms, we avoid saving any cluster state.
-                errorListener.accept(checkAndReportError(namespace, List.of(e.getMessage()), reservedStateVersion));
+                errorListener.accept(checkAndReportError(namespace, List.of(stackTrace(e)), reservedStateVersion));
             }
         });
     }