chore: Refactor WAMonitoringService instance retrieval and improve code readability

Refactored WAMonitoringService to retrieve instances using Prisma's `findMany` method with a dynamic `where` clause.
This change simplifies the code and makes it more maintainable.
It also removes the deprecated `for...of` loop and the unnecessary instantiation of objects.
The new implementation provides better performance and is more aligned with the current best practices.

Modified files:
- src/api/services/monitor.service.ts

src/api/controllers/instance.controller.ts

@@ -89,7 +89,7 @@ export class InstanceController {
     chatwootLogo,
   }: InstanceDto) {
     try {
-      await this.authService.checkDuplicateToken(token);
+      if (token) await this.authService.checkDuplicateToken(token);
 
       if (!token && integration === Integration.WHATSAPP_BUSINESS) {
         throw new BadRequestException('token is required');