[PLAT-18932]Disabling default region change via the operator

Summary:
We don't support changing the default region from the UI, ensuring we have same functionality using operator as well.

This restriction can be removed once we have evaluated and tested that we are supporting default region edits.

Test Plan: Tested locally

Reviewers: vkumar

Reviewed By: vkumar

Subscribers: yugaware

Differential Revision: https://phorge.dev.yugabyte.com/D48154

Author: Arpit-yb

managed/src/main/java/com/yugabyte/yw/common/operator/resources/universeCrd.yaml

@@ -43,10 +43,16 @@ spec:
               placementInfo:
                 description: Placement information for the universe.
                 type: object
+                x-kubernetes-validations:
+                  - message: defaultRegion cannot be removed once set.
+                    rule: has(self.defaultRegion) || !has(oldSelf.defaultRegion)
                 properties:
                   defaultRegion:
                     type: string
                     description: Default region for the universe.
+                    x-kubernetes-validations:
+                    - message: defaultRegion cannot be changed once set.
+                      rule: self == oldSelf
                   regions:
                     type: array
                     description: Regions for the universe.

managed/src/main/java/com/yugabyte/yw/common/operator/utils/OperatorUtils.java

@@ -416,12 +416,7 @@ public boolean checkIfPlacementInfoChanged(
     }
     JsonNode oldPlacementCloud = objectMapper.valueToTree(oldPlacementInfo.cloudList.get(0));
     JsonNode newPlacementCloud = objectMapper.valueToTree(ybUniverse.getSpec().getPlacementInfo());
-    if (oldPlacementCloud
-        .path("defaultRegion")
-        .asText()
-        .equals(newPlacementCloud.path("defaultRegion").asText())) {
-      return true;
-    }
+
     Map<String, JsonNode> oldRegions = mapByCode(oldPlacementCloud.path("regionList"));
     Map<String, JsonNode> newRegions = mapByCode(newPlacementCloud.path("regions"));