add login banner service

Modeled after the one from PVE, but using rust instead of perl for
resolving the nodename and writing to /etc/issue

Behavior differs a bit. We write all non-loopback addresses to this
file, as the gui accepts connections from them all, so limiting it to
the first one is not really sensible.
Further an error to resolve, or only getting loopback addresses won't
write out an empty /etc/issue file, but a note about the error at the
place where the address would be displayed.

Named it "pbsbanner", not "proxmox-backup-banner" as it's rather an
internal tool anyway and mirrors pvebanner, pmgbanner

Signed-off-by: Thomas Lamprecht <t.lamprecht@proxmox.com>

etc/Makefile

@@ -1,13 +1,16 @@
 include ../defines.mk
 
 UNITS := \
+	pbsbanner.service \
+
+DYNAMIC_UNITS := \
 	proxmox-backup.service \
 	proxmox-backup-proxy.service
 
-all: $(UNITS)
+all: $(UNITS) $(DYNAMIC_UNITS)
 
 clean:
-	rm -f $(UNITS)
+	rm -f $(DYNAMIC_UNITS)
 
 .SUFFIXES: .service.in .service
 .service.in.service:

etc/pbsbanner.service

@@ -0,0 +1,15 @@
+[Unit]
+Description=Proxmox Backup Server Login Banner
+ConditionPathExists=/usr/sbin/pbsbanner
+ConditionPathExists=!/usr/bin/pvebanner
+DefaultDependencies=no
+After=local-fs.target
+Before=console-getty.service
+
+[Service]
+ExecStart=/usr/sbin/pbsbanner
+Type=oneshot
+RemainAfterExit=yes
+
+[Install]
+WantedBy=getty.target