Add option to log service/task output to the console

Example:
    service log:console [2] /usr/sbin/udhcpd -f -- DHCP Server

Signed-off-by: Robert Andersson <robert.m.andersson@se.atlascopco.com>

docs/config.md

@@ -350,6 +350,7 @@ syslog using the native `logit` tool.  The full syntax is:
 
     log:/path/to/file
     log:prio:facility.level,tag:ident
+    log:console
     log:null
     log