Add "Test" to Notification Settings UI

[ogermer]

What problem does this feature solve or what does it enhance?

In the UI, Notification Settings allows for entering a notify URL for sending notifications. As a (new) user I cannot validate that this notification link is actually working

Proposed Solution

Creata a "Send Test Message" button to the UI that calls the URL as a POST message.

Also: Make the solution more generic by explaining in the UI and/or the documentation that an address with URL encoded parameters as a POST message (e.g. http://api.prowlapp.com/publicapi/add?apikey=<API_KEY>&priority=1&application=<APPLICATION_NAME>&event=<EVENT_LABEL>&description=<MESSAGE_TEXT>) is allowed.

Alternatives Considered

No response

[untitaker]

you can currently validate functionality by turning on the test heuristic which will produce warnings. a button that produces that warning directly is probably more convenient