Initial package for pnpr 0.1.0-alpha.5

Native binary taken from the @pnpm/pnpr.linux-{x64,arm64} npm platform
packages; systemd service with dynamic sysusers pnpr user. Storage in
/var/lib/pnpr, disposable proxy cache split into /var/cache/pnpr via
--cache. Default config proxies registry.npmjs.org; listen address and
extra flags via /etc/pnpr/pnpr.env.

pnpr.service

@@ -0,0 +1,39 @@
+[Unit]
+Description=pnpr - pnpm-compatible npm registry server
+Documentation=https://pnpm.io/pnpr
+After=network-online.target
+Wants=network-online.target
+ConditionPathExists=/etc/pnpr/pnpr.yaml
+
+[Service]
+Type=simple
+User=pnpr
+Group=pnpr
+
+# Hosted/published packages (config storage:) persist in /var/lib/pnpr;
+# the disposable mirror of upstream registries goes to /var/cache/pnpr
+# (--cache) and can be wiped at any time.
+StateDirectory=pnpr
+StateDirectoryMode=0750
+CacheDirectory=pnpr
+CacheDirectoryMode=0750
+
+EnvironmentFile=/etc/pnpr/pnpr.env
+ExecStart=/usr/bin/pnpr -c /etc/pnpr/pnpr.yaml --cache /var/cache/pnpr --listen ${PNPR_LISTEN} $PNPR_OPTS
+
+Restart=on-failure
+RestartSec=5s
+
+# Hardening
+NoNewPrivileges=yes
+ProtectSystem=strict
+ProtectHome=yes
+PrivateTmp=yes
+PrivateDevices=yes
+ProtectKernelTunables=yes
+ProtectKernelModules=yes
+ProtectControlGroups=yes
+RestrictAddressFamilies=AF_UNIX AF_INET AF_INET6
+
+[Install]
+WantedBy=multi-user.target