Create notification upon IMip message processing failure

[Juniar-Rakhman]

This is a follow up PR based on feedback on the original PR.

This is a follow up changes to a patch done for:
#10811

The patch to address above issue fixes the processing flow of iMip message processing. When a failure occurs, the batch job logs the error and continues processing the next iMIP message instead of failing the entire job.

Issue:
Although the patch resolves the processing problem, failures occur silently from the user’s perspective. The user is not informed when an iMIP message fails to process and therefore cannot take corrective action.

Solution:
Created a notification upon iMIP messaging failure that will be sent to message owner (account's email).

Added the following changes:

1. Error recovery with notification instead of failing silently.
2. Added sendErrorNotification() method to generate Nextcloud notification
3. Added a new notification subject 'imip_processing_failed' handled by the Mail app notifier.
4. When an error occurs, the user receives a Nextcloud notification explaining that the invitation could not be processed automatically.
5. The notification includes a direct link to the affected email, allowing the user to open it and manually add the calendar event.

[welcome]

Thanks for opening your first pull request in this repository! ✌️

[Juniar-Rakhman]

Here the notification is shown to the user.

When clicked, it will redirect the user to the failed email message.

For Users that do not use Nextcloud web, they might missed the notification, but they should receive the email about unread notifications after 1 hour (configurable).

Current setup is not so ideal as most IMip messages are time sensitive and most of our users do not use Nextcloud web.

I would prefer to be able to configure the notification like in the "activity" notification:

Probably a settings called "IMip Processing Failure" under "Other activities"

@ChristophWurst I could use your guidance here. I'm not sure if I should pursue further changes on Activity notification, and if so where do I start?