feat(Typebot): add splitMessages and timePerChar fields to Typebot models

- Introduced `splitMessages` and `timePerChar` fields in the Typebot and TypebotSetting models with default values.
- Created a migration script to update the database schema accordingly.
- Updated audio message handling to prepend `[audio]` to transcriptions for better clarity in message context.

src/api/integrations/chatbot/base-chatbot.controller.ts

@@ -280,7 +280,7 @@ export abstract class BaseChatbotController<BotType = any, BotData extends BaseC
       });
 
       if (!bot) {
-        throw new Error(`${this.integrationName} not found`);
+        return null;
       }
 
       return bot;