Guard: watch logs, ban misbehaving addresses in Housecarl

Files and the journal, patterns with one <IP>, bounties within a window,
bans in a Housecarl ban list with repeat offenders' bans growing; presets
for sshd, jarl, housecarl, steward, bind-xfr, postfix-sasl, dovecot,
nginx-auth and housecarl-drops; guard run/check/test/status/bans/ban/unban;
a Debian package with a sandboxed unit; an end-to-end test with Housecarl.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

testdata/presets/postfix-sasl.txt

@@ -0,0 +1,3 @@
+203.0.113.9	warning: unknown[203.0.113.9]: SASL LOGIN authentication failed: UGFzc3dvcmQ6
+203.0.113.9	warning: scanner.example.net[203.0.113.9]: SASL PLAIN authentication failed: authentication failure
+-	warning: hostname 203-0-113-9.example.net does not resolve to address 203.0.113.9