contrib: setup_templates: use write_file for the runner service

This results in the file being written unconditionally on every boot.
This also means that the file in cloud-init and the one in the machine
will not become out of sync.
The drawback is that we need to systemctl deamon-reload on every boot now,
which should however be okay performance-wise.

contrib/setup_templates/generic/cloud-init/user-data

@@ -14,42 +14,28 @@ write_files:
       ExecStart=
       ExecStart=-/sbin/agetty --autologin root --noclear %I $TERM
 
-runcmd:
-  - systemctl daemon-reload
-  - systemctl enable --now --no-block "[email protected]"
-  - |
-    set -e -u
-
-    # Set up a service that mounts the job config file system and runs the job
-    # script inside of it under the `runner` user.
-
-    SERVICE_FILE="github-action-runner.service"
-    SERVICE_PATH="/etc/systemd/system/${SERVICE_FILE}"
-
-    if ! test -e "${SERVICE_PATH}"
-    then
-        cat > "${SERVICE_PATH}" << 'EOF'
-    [Unit]
-    Description=GitHub JIT Runner
-    After=network.target cloud-final.service
-
-    [Service]
-    ExecStartPre=+/usr/bin/mount -o rw,fmask=0022,dmask=0022,uid=runner,gid=runner --mkdir /dev/disk/by-label/JOBDATA /home/runner/config
-    ExecStart=/home/runner/config/job.sh
-    ExecStopPost=+/usr/bin/systemctl poweroff
-    StandardOutput=journal+console
-    StandardError=journal+console
-    User=runner
-    WorkingDirectory=/home/runner
-    KillMode=process
-    KillSignal=SIGTERM
-    TimeoutStopSec=5min
+  - path: /etc/systemd/system/github-action-runner.service
+    content: |
+      [Unit]
+      Description=GitHub JIT Runner
+      After=network.target cloud-final.service
 
-    [Install]
-    WantedBy=cloud-init.target
-    EOF
+      [Service]
+      ExecStartPre=+/usr/bin/mount -o rw,fmask=0022,dmask=0022,uid=runner,gid=runner --mkdir /dev/disk/by-label/JOBDATA /home/runner/config
+      ExecStart=/home/runner/config/job.sh
+      ExecStopPost=+/usr/bin/systemctl poweroff
+      StandardOutput=journal+console
+      StandardError=journal+console
+      User=runner
+      WorkingDirectory=/home/runner
+      KillMode=process
+      KillSignal=SIGTERM
+      TimeoutStopSec=5min
+
+      [Install]
+      WantedBy=cloud-init.target
 
-        systemctl daemon-reload
-        systemctl enable "${SERVICE_FILE}"
-        systemctl start --no-block "${SERVICE_FILE}"
-    fi
+runcmd:
+  - systemctl daemon-reload
+  - systemctl enable --now --no-block [email protected]
+  - systemctl enable --now --no-block github-action-runner.service