fix: refactor correlation rule

Author: mjabascal10

backend/src/main/java/com/park/utmstack/service/dto/correlation/validators/CorrelationRuleValidator.java

@@ -22,9 +22,9 @@ public void validate(Object target, Errors errors) {
             errors.rejectValue("dataTypes", "DataTypesEmpty", "The rule must have at least one data type.");
         }
 
-        /*if (dto.getDefinition() == null || dto.getDefinition().getRuleVariables().isEmpty()) {
+        if (dto.getDefinition() == null || dto.getDefinition().getRuleVariables().isEmpty()) {
             errors.rejectValue("definition.ruleVariables", "RuleVariablesEmpty", "The rule must have at least one rule variable.");
-        }*/
+        }
 
         if (dto.getDefinition() != null && !StringUtils.hasText(dto.getDefinition().getRuleExpression())) {
             errors.rejectValue("definition.ruleExpression", "RuleExpressionEmpty", "The rule's expression must not be empty.");