s/pbsbanner/proxmox-backup-banner/ + move to /usr/lib

We want to avoid pbs if possible and also avoid placing internal
binaries, not intended for human direct use, in /bin or /sbin paths.

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

etc/proxmox-backup-banner.service.in

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