nixos/borgbackup: Add option `wrapper` (#447400)

nixos/modules/services/backup/borgbackup.nix

···
         ''
       );
 
+  # Returns a singleton list, due to usage of lib.optional
   mkBorgWrapper =
     name: cfg:
-    mkWrapperDrv {
+    lib.optional (cfg.wrapper != "" && cfg.wrapper != null) (mkWrapperDrv {
       original = lib.getExe config.services.borgbackup.package;
-      name = "borg-job-${name}";
+      name = cfg.wrapper;
       set = {
         BORG_REPO = cfg.repo;
       }
       // (mkPassEnv cfg)
       // cfg.environment;
-    };
+    });
 
   # Paths listed in ReadWritePaths must exist before service is started
   mkTmpfiles =
···
                 for the specified {option}`paths`.
               '';
               default = "root";
+            };
+
+            wrapper = lib.mkOption {
+              type = with lib.types; nullOr str;
+              description = ''
+                Name of the wrapper that is installed into {env}`PATH`.
+                Set to `null` or `""` to disable it altogether.
+              '';
+              default = "borg-job-${name}";
+              defaultText = "borg-job-<name>";
             };
 
             encryption.mode = lib.mkOption {
···
       environment.systemPackages = [
         config.services.borgbackup.package
       ]
-      ++ (lib.mapAttrsToList mkBorgWrapper jobs);
+      ++ (lib.flatten (lib.mapAttrsToList mkBorgWrapper jobs));
     }
   );
 }

nixos/tests/borgbackup.nix

···
               "--exclude-if-present"
               ".dont backup"
             ];
+
+            wrapper = "borg-main";
             postHook = "echo post";
             startAt = [ ]; # Do not run automatically
           };
···
             paths = dataDir;
             repo = localRepoMount;
             encryption.mode = "none";
+            wrapper = null;
             startAt = [ ];
           };
 
···
             "cat /mnt/borg/${dataDir}/${keepFile}"
         )
 
+        # Make sure custom wrapper name works
+        client.succeed("command -v borg-main")
+
     with subtest("localMount"):
         # the file system for the repo should not be already mounted
         client.fail("mount | grep ${localRepoMount}")
···
         # Make sure exactly one archive has been created
         assert int(client.succeed("{} list '${localRepoMount}' | wc -l".format(borg))) > 0
 
+        # Make sure disabling wrapper works
+        client.fail("command -v borg-job-localMount")
+
     with subtest("remote"):
         borg = "BORG_RSH='ssh -oStrictHostKeyChecking=no -i /root/id_ed25519' borg"
         server.wait_for_unit("sshd.service")
···
 
         # Make sure we can't access repos other than the specified one
         client.fail("{} list borg\@server:wrong".format(borg))
+
+        # Make sure default wrapper works
+        client.succeed("command -v borg-job-remote")
 
         # TODO: Make sure that data is actually deleted