Ability to Delete Custom Notification Categories for Messaging

[wayhappy138]

Description

Messaging custom notification categories keep track of all the senders (names and phone numbers) even if all the related messages were deleted, including from an archive.

Steps to reproduce:

• Open Owner Profile
• Open native Messaging App > Settings > Notifications
• Expand Others. Click on 'Show Unused Categories'
• There is list of Coversation / Notification categories with phone numbers and contact details. There is no way to delete categories, only to disable them.

If an item is deleted as a conversation (by clicking 'Not a conversation'), it would still be moved into 'Other' notification category with no ability to permanently delete them.

From a privacy perspective, it would be amazing to have:

1. An ability to delete existing custom notification categories.
2. Having custom categories to be automatically deleted if all related messages got deleted.
3. Have a global toggle 'Use conversation categories' to prevent them from being created in the first place, similar to the existing toggle 'Use notification history'.

Thank you for making GrapheneOS!