Add optional syslog logrus hook (#343)

* add optional syslog logrus hook

* document syslog

docs/configuration/syslog.md

@@ -0,0 +1,41 @@
+# Syslog
+
+GoToSocial can be configured to mirror logs to [syslog](https://en.wikipedia.org/wiki/Syslog), either via udp/tcp, or a local syslog (eg., `/var/log/syslog`).
+
+This is useful if you want to daemonize GtS and not handle log rotations etc yourself but rely on a proven implementation.
+
+Logs in syslog will look something like this:
+
+```text
+Dec 12 17:44:03 dilettante ./gotosocial[246860]: time=2021-12-12T17:44:03+01:00 level=info msg=connected to SQLITE database
+Dec 12 17:44:03 dilettante ./gotosocial[246860]: time=2021-12-12T17:44:03+01:00 level=info msg=there are no new migrations to run func=doMigration
+```
+
+## Settings
+
+```yaml
+#########################
+##### SYSLOG CONFIG #####
+#########################
+
+# Config for additional syslog log hooks. See https://en.wikipedia.org/wiki/Syslog,
+# and https://github.com/sirupsen/logrus/tree/master/hooks/syslog.
+#
+# These settings are useful when one wants to daemonize GoToSocial and send logs
+# to a specific place, either a local location or a syslog server. Most users will
+# not need to touch these settings.
+
+# Bool. Enable the syslog logging hook. Logs will be mirrored to the configured destination.
+# Options: [true, false]
+# Default: false
+syslog-enabled: false
+
+# String. Protocol to use when directing logs to syslog. Leave empty to connect to local syslog.
+# Options: ["udp", "tcp", ""]
+# Default: "tcp"
+syslog-protocol: "udp"
+
+# String. Address:port to send syslog logs to. Leave empty to connect to local syslog.
+# Default: "localhost:514"
+syslog-address: "localhost:514"
+```