nixos/switchable-system: remove default inhibitors and add release notes (#476820)

doc/release-notes/rl-2605.section.md

@@ -89,6 +89,8 @@
   If your SQLite database is corrupted, the migration might fail and require [manual intervention](https://github.com/louislam/uptime-kuma/issues/5281).
   See the [migration guide](https://github.com/louislam/uptime-kuma/wiki/Migration-From-v1-To-v2) for more information.
 
+- Switch inhibitors were introduced, which add a pre-switch check that compares a list of strings between the previous and the new generation, and refuses to switch into the new generation when there is a difference between the two lists. This allows to avoid switching into a system when for instance the systemd version changed by adding `config.systemd.package.version` to the switch inhibitors for your system. You can still forcefully switch into any generation by setting `NIXOS_NO_CHECK=1`.
+
 - The `services.nextcloud-spreed-signaling` NixOS module has been added to facilitate declarative management of a standalone Spreed signaling server ("High Performance Backend" for Nextcloud Talk).
 
 - `fetchPnpmDeps` and `pnpmConfigHook` were added as top-level attributes, replacing the now deprecated `pnpm.fetchDeps` and `pnpm.configHook` attributes.

nixos/modules/services/system/dbus.nix

@@ -174,10 +174,6 @@ in
         permissions = "u+rx,g+rx,o-rx";
       };
 
-      system.switch.inhibitors = [
-        cfg.dbusPackage
-      ];
-
       systemd.services.dbus = {
         aliases = [
           # hack aiding to prevent dbus from restarting when switching from dbus-broker back to dbus
@@ -216,10 +212,6 @@ in
         cfg.brokerPackage
       ];
 
-      system.switch.inhibitors = [
-        cfg.brokerPackage
-      ];
-
       # Just to be sure we don't restart through the unit alias
       systemd.services.dbus.reloadIfChanged = true;
       systemd.user.services.dbus.reloadIfChanged = true;

nixos/modules/system/boot/systemd.nix

@@ -567,10 +567,6 @@ in
       );
     };
 
-    system.switch.inhibitors = [
-      cfg.package
-    ];
-
     environment.systemPackages = [ cfg.package ];
 
     environment.etc =