Testing notifications should show response in a toast

[mabashian]

SUMMARY

In the old UI, when you tested a notification template we'd show the eventual response in a toast message. IIRC the toast would be green when the test was successful and red when it failed.

See the logic here: https://github.com/ansible/tower/blob/release_3.8.2/awx/ui/client/src/notifications/notification-templates-list/list.controller.js#L150-L174

There could be some overlap with #8853

[tiagodread]

Tests covered by 6059 we can close this issue once the test PR is merged.