[PLAT-14414] Enable Kubernetes provider validation by default

Summary: This change toggles the default value to true in reference.conf

Test Plan:
Deployed YBA with this setting and tried to create invalid
provider. It went trough validation as expected.

Reviewers: anijhawan, svarshney

Reviewed By: svarshney

Subscribers: yugaware

Differential Revision: https://phorge.dev.yugabyte.com/D35996

managed/src/main/resources/reference.conf

@@ -213,7 +213,7 @@ yb {
     # This can contain comma separated values, like "/,/tmp,"
     monitored_mount_roots = "/"
     vm_os_patching = true
-    kubernetes_provider_validation = false
+    kubernetes_provider_validation = true
     azure_provider_validation = true
     gcp_provider_validation = true
   }