nixos/podman: Introduce new option extraRuntimes

This disables the hard, not overridable, dependency on `runc`.
It also sharpens the description of `extraPackages` to highlight the
difference between those options.

Fixes #443274.

nixos/modules/virtualisation/podman/default.nix

@@ -103,13 +103,24 @@ in
     extraPackages = mkOption {
       type = with types; listOf package;
       default = [ ];
+      description = ''
+        Extra dependencies for podman to be placed on $PATH in the wrapper.
+      '';
+    };
+
+    extraRuntimes = mkOption {
+      type = with types; listOf package;
+      # keep the default in sync with the podman package
+      default = lib.optionals pkgs.stdenv.hostPlatform.isLinux [ pkgs.runc ];
+      defaultText = lib.literalExpression ''lib.optionals pkgs.stdenv.hostPlatform.isLinux [ pkgs.runc ]'';
       example = lib.literalExpression ''
         [
           pkgs.gvisor
         ]
       '';
       description = ''
-        Extra packages to be installed in the Podman wrapper.
+        Extra runtime packages to be installed in the Podman wrapper.
+        Those are then placed in libexec/podman, i.e. are seen as podman internal commands.
       '';
     };
 
@@ -161,21 +172,20 @@ in
                 config.systemd.package # To allow systemd-based container healthchecks
               ]
               ++ lib.optional (config.boot.supportedFilesystems.zfs or false) config.boot.zfs.package;
-            extraRuntimes = [
-              pkgs.runc
-            ]
-            ++
-              lib.optionals
-                (
-                  config.virtualisation.containers.containersConf.settings.network.default_rootless_network_cmd or ""
-                  == "slirp4netns"
-                )
-                (
-                  with pkgs;
-                  [
-                    slirp4netns
-                  ]
-                );
+            extraRuntimes =
+              cfg.extraRuntimes
+              ++
+                lib.optionals
+                  (
+                    config.virtualisation.containers.containersConf.settings.network.default_rootless_network_cmd or ""
+                    == "slirp4netns"
+                  )
+                  (
+                    with pkgs;
+                    [
+                      slirp4netns
+                    ]
+                  );
           };
       };