Fix Messaging sync upsert in messageChannel association (#9880)

We have recently changed an .insert into a .upsert but we forgot to add
the unique index on the postgres schema.

packages/twenty-server/src/modules/messaging/message-import-manager/services/messaging-message.service.ts

@@ -65,7 +65,7 @@ export class MessagingMessageService {
             messageExternalId: message.externalId,
             messageThreadExternalId: message.messageThreadExternalId,
           },
-          ['messageChannelId'],
+          ['messageChannelId', 'messageId'],
           transactionManager,
         );