feature(SMTP): Make it possible to choose between TLS, StartTLS et insecure SMTP connection

[alexandrebouthinon]

What does this PR do ?

Add the feature allowing developer to choose between insecure, TLS or StartTLS connection where instantiating a new SMTP client from the Hermes Plugin

hermesMessengerPlugin.clients.smtp.addAccount(
  "common",
  "smtp.example.com",
  587,
  "dummyUser",
  "dummyPass",
  "[email protected]",
  SMTPClientSSLMode.NONE
);

hermesMessengerPlugin.clients.smtp.addAccount(
  "starttls",
  "smtp.example.com",
  587,
  "dummyUser",
  "dummyPass",
  "[email protected]",
  SMTPClientSSLMode.STARTTLS
);

hermesMessengerPlugin.clients.smtp.addAccount(
  "tls",
  "smtp.example.com",
  465,
  "dummyUser",
  "dummyPass",
  "[email protected]",
  SMTPClientSSLMode.TLS
);