Add ability to test notification publishers

[2000rosser]

Description

Add a button to the notifications settings to test the publisher.

Back-end implementation: https://github.com/DependencyTrack/dependency-track/pull/3983

Addressed Issue

https://github.com/DependencyTrack/dependency-track/issues/2924

Checklist

• [x] I have read and understand the contributing guidelines
• [ ] This PR introduces new or alters existing behavior, and I have updated the documentation accordingly