added SMTP monitor

[koehn]

Tick the checkbox if you understand [x]:

• I have read and understand the pull request rules.

Description

Add SMTP monitor

This allows users to monitor SMTP/SMTPS servers. They can optionally verify STARTTLS settings, or for SMTPS, they can just verify the TLS.

Type of change

Please delete any options that are not relevant.

• New feature (non-breaking change which adds functionality)

Checklist

• My code follows the style guidelines of this project
• I ran ESLint and other linters for modified files
• I have performed a self-review of my own code and tested it
• I have commented my code, particularly in hard-to-understand areas (including JSDoc for methods)
• My changes generates no new warnings
• My code needed automated testing. I have added them (this is optional task)

Screenshots (if any)

[ShadowGaming100]

+1