Add SmtpAuthHealthCheck

[tylerwoonton]

What is the feature?

We should add an SmtpAuthHealthCheck to the package.

What benefits will this change bring?

This will be used broadly across various apps, so is worth including in the core package.

Additional context

• The check should try and connect to the configured SMTP server and expect to receive an SMTP EHLO response.
• It should also then attempt to perform auth against the server, using configured credentials e.g. https://www.ndchost.com/wiki/mail/test-smtp-auth-telnet
• If either of these do not complete successfully, the check should fail.
• A relevant and detailed error message should be presented back in the JSON data.