feat(django-apps): Add timers option

This is similar to extraServices but without the partOf, upheldBy and
wantedBy settings.

modules/nixos/django-apps/default.nix

@@ -322,6 +322,15 @@ in
                   Extra services to run in parallel of the application.
                   May be used to run background tasks and/or workers.
                 '';
+
+                timers = mkOption {
+                  type = attrs;
+                  default = { };
+                  description = ''
+                    Extra oneshot services to run in parallel of the application.
+                    Be aware that `startAt` should be included.
+                  '';
+                };
               };
 
               manageScript = mkOption {
@@ -805,6 +814,28 @@ in
               } serviceContent
             )
           ) config.extraServices)
+          // (mapAttrs' (
+            serviceName: serviceContent:
+            nameValuePair "dj-${name}_${serviceName}" (
+              recursiveUpdate {
+                inherit after environment path;
+
+                serviceConfig = {
+                  inherit
+                    Group
+                    LoadCredential
+                    RuntimeDirectory
+                    StateDirectory
+                    UMask
+                    User
+                    ;
+
+                  WorkingDirectory = "/var/lib/django-apps/${name}/source";
+                  DynamicUser = true;
+                };
+              } serviceContent
+            )
+          ) config.timers)
         ) cfg.sites);
     };