Switch to a templated systemd unit

systemd's user services are too immature.

See #1771

Author: nhooyr

ci/build/code-server.service

@@ -6,6 +6,7 @@ After=network.target
 Type=exec
 ExecStart=/usr/bin/code-server
 Restart=always
+User=%i
 
 [Install]
 WantedBy=default.target

ci/build/nfpm.yaml

@@ -12,5 +12,5 @@ homepage: "https://github.com/cdr/code-server"
 license: "MIT"
 files:
   ./ci/build/code-server-nfpm.sh: /usr/bin/code-server
-  ./ci/build/code-server.service: /usr/lib/systemd/user/code-server.service
+  ./ci/build/code-server.service: /usr/lib/systemd/system/code-server.service
   ./release-standalone/**/*: "/usr/lib/code-server/"