Add provider data to notifications (#14104)

## Summary

**What** —
Add a providerData field to notifications

**Why** —
We need the ability to pass dynamic fields to specific providers. E.g. CC and BCC for emails

**How** —
Just adding the field to the model

**Testing** —
Added the field to existing tests

## Checklist

Please ensure the following before requesting a review:

- [x] I have added a **changeset** for this PR
    - Every non-breaking change should be marked as a **patch**
    - To add a changeset, run `yarn changeset` and follow the prompts
- [x] The changes are covered by relevant **tests**
- [x] I have verified the code works as intended locally
- [ ] I have linked the related issue(s) if applicable



---

> [!NOTE]
> Adds `provider_data` to notifications (types, workflow input, DB model/migration) and forwards it in the Medusa Cloud Email provider, with tests updated accordingly.
> 
> - **Data/Schema**:
>   - Add `provider_data` (`jsonb`) to `notification` model and DB via migration `Migration20251121150408` and snapshot update.
> - **Types/DTOs**:
>   - Add optional `provider_data` to `CreateNotificationDTO`, `NotificationDTO`, and `ProviderSendNotificationDTO`.
> - **Workflows**:
>   - Extend `send-notifications` step input with `provider_data`.
> - **Providers**:
>   - Medusa Cloud Email: include `provider_data` in outgoing request payload.
> - **Tests**:
>   - Update integration tests to pass and assert `provider_data` propagation.
> - **Changeset**:
>   - Patch bumps for `@medusajs/notification`, `@medusajs/core-flows`, `@medusajs/types`.
> 
> <sup>Written by [Cursor Bugbot](https://cursor.com/dashboard?tab=bugbot) for commit 6f114c75c974a145ef60213637d7c41bc605a0bf. This will update automatically on new commits. Configure [here](https://cursor.com/dashboard?tab=bugbot).</sup>

packages/modules/notification/src/models/notification.ts

@@ -13,6 +13,8 @@ export const Notification = model.define("notification", {
   template: model.text().nullable(),
   // The data that gets passed over to the provider for rendering the notification.
   data: model.json().nullable(),
+  // Additional data specific to the channel or provider. For example, cc and bcc for emails.
+  provider_data: model.json().nullable(),
   // This can be the event name, the workflow, or anything else that can help to identify what triggered the notification.
   trigger_type: model.text().nullable(),
   // The ID of the resource this notification is for, if applicable. Useful for displaying relevant information in the UI