feat: add OSS offsite backup gate

deploy/server/platform-offsite-backup.service

@@ -0,0 +1,18 @@
+[Unit]
+Description=Copy encrypted data terminal cloud backup to OSS
+Requires=network-online.target
+After=network-online.target platform-backup.service
+
+[Service]
+Type=oneshot
+User=root
+Group=root
+UMask=0077
+Environment=BACKUP_ROOT=/var/backups/data-terminal-cloud
+Environment=OFFSITE_STATE_DIR=/var/lib/data-terminal-cloud-offsite
+Environment=OFFSITE_CONFIG_FILE=/etc/data-terminal-cloud/offsite-backup.env
+ExecStart=/opt/data-terminal-cloud/current/deploy/server/sync-backup-offsite.sh
+Nice=10
+NoNewPrivileges=true
+PrivateTmp=true
+TimeoutStartSec=4h