Deleted notifications being send by kube-notifier-controller

[tiej-dr]

Describe the bug
When a notification is deleted it's not reflected in "kube-notifier-controller" - resulting in notifications being send after deletion.

To Reproduce

1. Create notification. E.g
   kubectl apply -f hello-notifier.yaml -n hello-app
   .. trigger notification condition to check a notification is send.

2. Delete notification:
   kubectl delete notifications.argoproj.io hello-notifier -n hello-app

3. Trigger notification condition again, resulting in notification is being send again, even if it's been deleted.

Expected behavior
When a given notification is deleted, kube-notifier-controller should not send any notifications of given kind.

Additional context
In order to update "kube-notifier-controller" with latest changes (notification deletion), i had to restart controller manually (by deleting pod)

[sarabala1979]

@tiej-dr do you like to contribute?

[tiej-dr]

@tiej-dr do you like to contribute?

@sarabala1979 , haven't much of golang experience, and not sure how much time I will have for it, but if you have time to set me up and point me in the right direction I'm willing to give it a try.