feat: add automation condition to filter private notes (#12102)

## Summary

Adds a new automation condition to filter private notes.

This allows automation rules to explicitly include or exclude private
notes instead of relying on implicit behavior.

Fixes: #11208 

## Preview



https://github.com/user-attachments/assets/c40f6910-7bbf-4e59-aae5-ad408602927a

spec/services/automation_rules/condition_validation_service_spec.rb

@@ -10,7 +10,8 @@ RSpec.describe AutomationRules::ConditionValidationService do
         rule.conditions = [
           { 'values': ['open'], 'attribute_key': 'status', 'query_operator': nil, 'filter_operator': 'equal_to' },
           { 'values': ['+918484'], 'attribute_key': 'phone_number', 'query_operator': 'OR', 'filter_operator': 'contains' },
-          { 'values': ['test'], 'attribute_key': 'email', 'query_operator': nil, 'filter_operator': 'contains' }
+          { 'values': ['test'], 'attribute_key': 'email', 'query_operator': 'OR', 'filter_operator': 'contains' },
+          { 'values': [true], 'attribute_key': 'private_note', 'query_operator': nil, 'filter_operator': 'equal_to' }
         ]
         rule.save
       end

spec/services/automation_rules/conditions_filter_service_spec.rb

@@ -83,6 +83,27 @@ RSpec.describe AutomationRules::ConditionsFilterService do
         end
       end
 
+      context 'when filtering private notes' do
+        before do
+          rule.conditions = [
+            { 'values': [true], 'attribute_key': 'private_note', 'query_operator': nil, 'filter_operator': 'equal_to' }
+          ]
+          rule.save
+        end
+
+        it 'will return true when the message is a private note' do
+          message.update!(private: true)
+
+          expect(described_class.new(rule, conversation, { message: message, changed_attributes: {} }).perform).to be(true)
+        end
+
+        it 'will return false when the message is not a private note' do
+          message.update!(private: false)
+
+          expect(described_class.new(rule, conversation, { message: message, changed_attributes: {} }).perform).to be(false)
+        end
+      end
+
       context 'when filter_operator is on processed_message_content' do
         before do
           rule.conditions = [