Add print server for label printer to have it easily usable via SSH

Add and configure a print server for the Brother P-touch QL 500 label
printer, so that it can be easily used via SSH.

Do the following to make that work:
- Configure the print server host.
- Package printer-driver-ptouch to have a working driver for the label
  printer.
- Configure CUPS.
- Add a script "forcecommand-lpr-wrapper", which works together with the
  ForceCommand sshd_config option and wraps lpr to provide an easy
  interface to use the Brother QL 500 label printer via SSH.
- Add a print user and configure SSH to have the
  "forcecommand-lpr-wrapper" script accessible without a password using
  the print user via SSH.

flake.nix

@@ -197,6 +197,20 @@
             ./config/hosts/forgejo-actions-runner
           ];
         };
+
+        ptouch-print-server = {
+          deployment = {
+            targetHost = "ptouch-print-server.z9.ccchh.net";
+            targetPort = 22;
+            targetUser = "colmena-deploy";
+            tags = [ "thinkcccluster" ];
+          };
+          imports = [
+            ./config/common
+            ./config/proxmox-vm
+            ./config/hosts/ptouch-print-server
+          ];
+        };
       };
 
       packages.x86_64-linux = {