Revise unsubscribe options in user profile notifications form

[Vitaliy-1]

Describe the problem
In user profile -> notifications, there are options to enable/disable certain notification types, which are no longer shown to the end user.

There are 3 notification levels, from which only the NOTIFICATION_LEVEL_TASK is displayed in the user's taskbar. Some are shown in banners on certain submission workflow stages, e.g.:

pkp-lib/controllers/tab/workflow/PKPWorkflowTabHandler.php

Line 119 in 6c70926

Notification::NOTIFICATION_LEVEL_NORMAL => [

but most of the notifications with unsubscribe option aren't displayed anywhere in the system and are used to be sent with an email. This means that there is no need for the existing of the 2 options - enable notification and unsubscribe from email, in particular, for:

• A new announcement has been created (NOTIFICATION_TYPE_NEW_ANNOUNCEMENT)
• An issue has been published (NOTIFICATION_TYPE_PUBLISHED_ISSUE)
• A new article, "Title," has been submitted (NOTIFICATION_TYPE_SUBMISSION_SUBMITTED)
• Weekly email of outstanding tasks (NOTIFICATION_TYPE_EDITORIAL_REMINDER)
• Statistics report summary (NOTIFICATION_TYPE_EDITORIAL_REPORT)

To Reproduce
Steps to reproduce the behavior:

1. Go to Announcements and create a new one
2. Publish it with the option to send a notification to all registered user
3. Log in as a user, who is subscribed to see new announcement notifications
4. See that this notification isn't displayed anywhere in the interface, only email is sent

What application are you using?
OJS main branch

[NateWr]

I'd prefer to solve this alongside a complete rewrite of the unsubscribe settings. In my opinion, the existing approach to "tasks" needs to be rethought, inline with the recommendations for an activity feed in #5729. There is no need to allow the user to unsubscribe from in-app notifications -- only emails. So the whole UI and the underlying data structure could be simplified to focus on email subscriptions.