dev: email notifications (#3421)

* dev: create email notification preference model

* dev: intiate models

* dev: user notification preferences

* dev: create notification logs for the user.

* dev: email notification stacking and sending logic

* feat: email notification preference settings page.

* dev: delete subscribers

* dev: issue update ui implementation in email notification

* chore: integrate email notification endpoint.

* chore: remove toggle switch.

* chore: added labels part

* fix: refactored base design with tables

* dev: email notification templates

* dev: template updates

* dev: update models

* dev: update template for labels and new migrations

* fix: profile settings preference sidebar.

* dev: update preference endpoints

* dev: update the schedule to 5 minutes

* dev: update template with priority data

* dev: update templates

* chore: enable `issue subscribe` button for all users.

* chore: notification handling for external api

* dev: update origin request

---------

Co-authored-by: Prateek Shourya <prateekshourya29@gmail.com>
Co-authored-by: LAKHAN BAHETI <lakhanbaheti9@gmail.com>
Co-authored-by: Ramesh Kumar Chandra <rameshkumar2299@gmail.com>
Co-authored-by: NarayanBavisetti <narayan3119@gmail.com>

apiserver/plane/settings/common.py

@@ -291,6 +291,7 @@ CELERY_IMPORTS = (
     "plane.bgtasks.issue_automation_task",
     "plane.bgtasks.exporter_expired_task",
     "plane.bgtasks.file_asset_task",
+    "plane.bgtasks.email_notification_task",
 )
 
 # Sentry Settings