[Enhancement] Invoke test alert for SMTP + improvements to SMTP configuration

[aelkugia]

Test alert for SMTP:

There should be a way to test whether SMTP alerting is working properly. Some functionality to invoke a test alert to see if SMTP is indeed set up correctly. Currently, customers are configuring SMTP, but are not entirely certain if the set up has been correct.

SMTP configuration improvements:

Separately, customers find it hard to configure SMTP alerting if their SMTP server isn’t set up to use authentication, because the configuration asks for a username and password.

@r0mant feel free to add more context to this

[benarent]

It might also be useful to just provide an API endpoint via Hosted Email clients ( but in a provider agonistic manor ), and also provide a full suite of user controllable test commands.