Added email notification upon iMIP message processing failure

[Juniar-Rakhman]

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 an email 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 email body containing instruction for the user on what to do. Also contains technical details on the errors
3. Email notification will be sent to the account's owner.
4. The email contains original message attached so the user can add it manually to their calendar.

[Juniar-Rakhman]

This is the email received by the user upon iMIP processing failure (tested on our test server)

The code changes are currently running in one of our production environments and are functioning as expected. Users are now notified when this type of error occurs.

[SebastianKrupinski]

Hi @Juniar-Rakhman

Thank you for the PR.

I don't know if sending the user another email is the best way... what if we created a system notification with a link to the actual failed email?

[Juniar-Rakhman]

Hi @SebastianKrupinski

That was my initial thoughts too. But not all of our users use nextcloud web.
Most of them are using their own email/calendar clients e.g. thunderbird, mac mail/calendar etc. So email is the only way we could ensure that they get this notification.

[ChristophWurst]

Thank you for the pull request @Juniar-Rakhman!

Informing the user makes sense. I would just request that this should happen as a Nextcloud notification with user settings. Default should be to receive a notification and no email.
Admins will be able to change defaults, and users can change the setting to their liking.

https://docs.nextcloud.com/server/latest/developer_manual/digging_deeper/notifications.html

[Juniar-Rakhman]

@ChristophWurst Thank you for the feedback.

I’ll switch this to a Nextcloud notification with user settings, defaulting to in-app notifications (no email). I will update the PR accordingly.

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