docs: Clarified Agent Assist max retention is 30 days

PiperOrigin-RevId: 489241089

google/cloud/dialogflow/cx/v3/security_settings.proto

@@ -323,12 +323,11 @@ message SecuritySettings {
   // purged due to retention policy, we may still hold it in backup storage for
   // a few days without allowing direct readings.
   oneof data_retention {
-    // Retains data in interaction logging for the specified number of days.
-    // This does not apply to Cloud logging, which is owned by the user - not
-    // Dialogflow.
-    // User must set a value lower than Dialogflow's default 365d TTL (time to
-    // live). Setting a value higher than that has no effect. A missing value or
-    // setting to 0 also means we use Dialogflow's default TTL.
+    // Retains the data for the specified number of days.
+    // User must set a value lower than Dialogflow's default 365d TTL (30 days
+    // for Agent Assist traffic), higher value will be ignored and use default.
+    // Setting a value higher than that has no effect. A missing value or
+    // setting to 0 also means we use default TTL.
     int32 retention_window_days = 6;
   }