nixos/power-management: deprecate powerUpCommands

Their ordering is ill-defined. Users are better off using an explicit systemd service.

nixos/modules/config/power-management.nix

@@ -62,6 +62,19 @@ in
 
   config = lib.mkIf cfg.enable {
 
+    warnings = lib.optional (cfg.powerUpCommands != "") ''
+      powerManagement.powerUpCommands is deprecated due to it having unclear ordering semantics.
+      It will be removed in NixOS 26.11.
+      It is recommended to create an explicit systemd oneshot service instead,
+      that is pulled in at the right time during the boot process.
+      See https://www.freedesktop.org/software/systemd/man/latest/systemd.special.html
+      for more information on possible targets that can be used for this.
+
+      If you also want to run this service upon waking up from resume, the recommended
+      method to do so is described here:
+      https://www.freedesktop.org/software/systemd/man/latest/systemd.special.html#sleep.target
+    '';
+
     systemd.targets.post-resume = {
       description = "Post-Resume Actions";
       requires = [ "post-resume.service" ];
@@ -85,8 +98,8 @@ in
       description = "Post-boot Actions";
       # It's not well defined at what point in the bootup sequence this should run
       # we should eventually just remove this.
-      after = [ "multi-user.target" ];
       wantedBy = [ "multi-user.target" ];
+      restartIfChanged = false;
       serviceConfig = {
         Type = "oneshot";
         RemainAfterExit = true;