Improve notifier part

[defelmnq]

In order for the OOM and OOD notifications to work - we need to change a bit the notifiers :

• Create a new migration to add the template for the new events. It is a simple DB migration.
• Modify both the FE and BE to add a new event with the preferences.
  • It should be done in the admin side to let admins choose if the notifications should be sent through webhooks or email
  • It should be done in the user side to let users turn it on or off.

⚠ This component is the last one that should be merged - once merged the connection between the processing part and the notifiers can be done.