- Create Notifications module and NotificationType model
- Start migration for adding notifications
- No functionalities added yet only template code

…is sent

notification entry

Changes:
* Replaced is_enable to is_enabled for Notification Preferences
* Update default is_enabled to true for Notifcation Types

`import_config` must always appear at the bottom for environment
specific configurations to be applied correctly. All configurations
after this line will overwrite configurations that exists in the
environment specific ones.

- remove auto-generated controllers and views that are not used

If user preference has no time option, use the time_option from
notification_config instead. This is so that the behaviour of these
users with no preferences would always follow the default chosen by the
course admin

…/Santosh3007/source-academy-backend into add-avenger-backlog-notification

Oban introduced changes to testing in v2.12, this commit changes the old
test configurations to the new one recommended by official docs.

…/Santosh3007/source-academy-backend into add-avenger-backlog-notification

…/Santosh3007/source-academy-backend into add-avenger-backlog-notification

Current nus users will have their email attribute populated based on
their username. nus users are identified from the provider attribute.

Future nus users will have their email attribute populated on creation
ideally.

- move mailing logic to notification worker
- insert into sent_notifications when email is sent out successfully

- move guard clauses to prevent unnecessary querying

* Notification configs now return course and notification preferences

* Query returns an array of preferences per config due to LEFT OUTER
  JOIN, the change ensures either nil or the first preference is
  returned
* It is guaranteed there is maximally one preference in the array due to
  the unique constraint in the new migration

- Add put upsert time options endpoints
- Fix changeset issues with upsert noti config endpoints

* Removed extra unused route