Add icon select to manual trigger (#12724)

## After

<img width="1220" alt="image"
src="https://github.com/user-attachments/assets/98a73aae-80d7-4e92-93d3-be13210da88b"
/>

<img width="1131" alt="image"
src="https://github.com/user-attachments/assets/9919e415-4355-4995-8979-9055b821f1e9"
/>

<img width="1300" alt="image"
src="https://github.com/user-attachments/assets/27f11cb3-d72c-468a-a641-8414172b9b54"
/>

<img width="1353" alt="image"
src="https://github.com/user-attachments/assets/2f0037f2-fe17-48b6-b7e6-c7528687a5fd"
/>

packages/twenty-front/src/modules/workflow/validation-schemas/workflowSchema.ts

@@ -206,6 +206,7 @@ export const workflowManualTriggerSchema = baseTriggerSchema.extend({
   settings: z.object({
     objectType: z.string().optional(),
     outputSchema: z.object({}).passthrough(),
+    icon: z.string().optional(),
   }),
 });