feat: add --outgoing-ignore-tls to keep the relay off STARTTLS (#377)

The relay connection only had `secure`, so with `secure: false` nodemailer
still upgraded to STARTTLS whenever the server advertised it, and there was
no way to talk cleartext to such a server. Pass nodemailer's `ignoreTLS`
through as `ignoreTLS` on the relay config, wired to
--outgoing-ignore-tls / MAILDEV_OUTGOING_IGNORE_TLS / `outgoingIgnoreTls`.

.changeset/outgoing-ignore-tls.md

@@ -0,0 +1,8 @@
+---
+'@maildev/smtp': patch
+'maildev': patch
+---
+
+Add `--outgoing-ignore-tls` / `MAILDEV_OUTGOING_IGNORE_TLS` (`outgoingIgnoreTls`,
+`ignoreTLS` on the relay config) to keep the outgoing relay connection on
+cleartext even when the server advertises STARTTLS (#377).