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

app/javascript/dashboard/routes/dashboard/settings/automation/constants.js

@@ -14,6 +14,12 @@ export const AUTOMATIONS = {
         inputType: 'search_select',
         filterOperators: OPERATOR_TYPES_1,
       },
+      {
+        key: 'private_note',
+        name: 'PRIVATE_NOTE',
+        inputType: 'search_select',
+        filterOperators: OPERATOR_TYPES_1,
+      },
       {
         key: 'content',
         name: 'MESSAGE_CONTAINS',