CSPL-4024: Enchance IDXC upgrade error message. (#1594)

* Add explanation for error status.

* Remove outer If statement

* Move goto IndexerCluster back

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Co-authored-by: igor.grzankowski <@splunk.com>

Author: Igor-splunk

pkg/splunk/enterprise/upgrade.go

@@ -137,8 +137,11 @@ ClusterManager:
 
 		// check if an image upgrade is happening and whether CM has finished updating yet, return false to stop
 		// further reconcile operations on custom resource until CM is ready
-		if clusterManager.Status.Phase != enterpriseApi.PhaseReady || cmImage != spec.Image {
-			return false, nil
+		if clusterManager.Status.Phase != enterpriseApi.PhaseReady {
+			return false, fmt.Errorf("cluster manager %s is not ready (phase: %s). IndexerCluster upgrade is waiting for ClusterManager to be ready", clusterManager.Name, clusterManager.Status.Phase)
+		}
+		if cmImage != spec.Image {
+			return false, fmt.Errorf("cluster manager %s image (%s) does not match IndexerCluster image (%s). Please upgrade ClusterManager and IndexerCluster together using the operator's RELATED_IMAGE_SPLUNK_ENTERPRISE or upgrade the ClusterManager first", clusterManager.Name, cmImage, spec.Image)
 		}
 		goto IndexerCluster
 	}