Suggestion: add security/cy2-plain as a dependency of mail/postfix sasl option

[manphiz <manphiz%gmail.com@localhost>]

Hi,

I was trying to set up postfix as a mail relay for Gmail.  It turns
out the postfix shipped with the system was not compiled with
cyrus-sasl support.  So I tried to build mail/postfix from pkgsrc with
the sasl option.  It successfully brought in cyrus-sasl as a build
dependency, but it still didn't work and failed with this message[1].
It's not until I found this blog[2] until I realized that I needed to
also compile and install security/cy2-plain for this to work.

I'd like to suggest adding security/cy2-plain, or better with other
authentication methods like security/cy2-digestmd5 and
security/cy2-crammd5 for the sasl to work out of the box.  This may
save users to go through this effort again to make postfix work with
Gmail and other mail providers.

Thanks.

[1] Dec 19 20:40:48 yeeloong-netbsd postfix/smtp[21224]: 222C722E15C:
to=<manphiz%gmail.com@localhost>, relay=smtp.gmail.com[74.125.137.109]:587,
delay=21564, delays=21563/0.68/0.51/0, dsn=4.7.0, status=deferred
(SASL authentication failed; cannot authenticate to server
smtp.gmail.com[74.125.137.109]: no mechanism available)
[2] https://www.lonsteins.com/posts/netbsd-postfix-relaying-and-sasl/