UI Email Notification missing success feedback

[DavidePrincipi]

When Email Notification settings are saved successfully a task completion feedback is missing:

Discussion https://mattermost.nethesis.it/nethesis/pl/hs98inr3ujyxjekoj1e8xztk7e

[stephdl]

QA

version to test is 3.7.0-dev.3

Once the testing version is installed, setup a smarthost in your cluster, you get a green (OK) notification toaster when you save the form

[mrmarkuz]

Test case verified

• A notification "Set smarthost settings" is shown when the notification settings are saved.