Prefix lines in DebugWriter with CLIENT and SERVER

[arp242]

Strictly this isn't needed since client commands are in the form "verb arguments" and server replies are in the form "numeric-code text". But not everyone is intimately familiar with SMTP, and even if you are, IMHO the CLIENT/SERVER prefixes makes the output a lot easier to scan.

Full example:

220 smtp.fastmail.com ESMTP ready
EHLO localhost
250-smtp.fastmail.com
250-PIPELINING
250-SIZE 71000000
250-ENHANCEDSTATUSCODES
250-8BITMIME
250 AUTH PLAIN LOGIN XOAUTH2 OAUTHBEARER
AUTH LOGIN QyxzeSdXKiJDMwo=
334 UGFzc3dvcmQ6
VEordkp6dEhYPAo=
235 2.0.0 OK
MAIL FROM:<from@arp242.net> BODY=8BITMIME
250 2.1.0 Ok
RCPT TO:<to@arp242.net>
250 2.1.5 Ok
DATA
354 End data with <CR><LF>.<CR><LF>
From: from@arp242.net
To: to@arp242.net
Subject: test

Test
.
250 2.0.0 Ok: queued as 40BECEC0498 5F5864B5217 via phl-compute-03
QUIT
221 2.0.0 Bye

Becomes:

SERVER  220 smtp.fastmail.com ESMTP ready
CLIENT  EHLO localhost
SERVER  250-smtp.fastmail.com
SERVER  250-PIPELINING
SERVER  250-SIZE 71000000
SERVER  250-ENHANCEDSTATUSCODES
SERVER  250-8BITMIME
SERVER  250 AUTH PLAIN LOGIN XOAUTH2 OAUTHBEARER
CLIENT  AUTH LOGIN QyxzeSdXKiJDMwo=
SERVER  334 UGFzc3dvcmQ6
CLIENT  VEordkp6dEhYPAo=
SERVER  235 2.0.0 OK
CLIENT  MAIL FROM:<from@arp242.net> BODY=8BITMIME
SERVER  250 2.1.0 Ok
CLIENT  RCPT TO:<to@arp242.net>
SERVER  250 2.1.5 Ok
CLIENT  DATA
SERVER  354 End data with <CR><LF>.<CR><LF>
CLIENT  From: from@arp242.net
CLIENT  To: to@arp242.net
CLIENT  Subject: test
CLIENT
CLIENT  Test
CLIENT  .
SERVER  250 2.0.0 Ok: queued as 7899B14002F7 7BE7C338A76 via phl-compute-01
CLIENT  QUIT
SERVER  221 2.0.0 Bye