remove lots of dead code and refactor

modules/containerization.nix

@@ -0,0 +1,35 @@
+{
+  config,
+  lib,
+  ...
+}:
+let
+  cfg = config.my.containerization;
+in
+{
+  options.my.containerization = {
+    enable = lib.mkEnableOption "containerization";
+    usePodman = lib.mkOption {
+      type = lib.types.bool;
+      default = true;
+      description = "whether to use podman instead of docker";
+    };
+  };
+
+  config = lib.mkIf cfg.enable {
+    virtualisation = {
+      containers.enable = true;
+      podman = lib.mkIf cfg.usePodman {
+        enable = true;
+        # create 'docker' alias for podman, to use as
+        # drop-in replacement
+        dockerCompat = true;
+        defaultNetwork.settings = {
+          dns_enabled = true;
+          ipv6_enabled = true;
+        };
+      };
+      oci-containers.backend = lib.mkIf cfg.usePodman "podman";
+    };
+  };
+}

modules/default.nix

@@ -5,5 +5,6 @@
     ./caddy.nix
     ./roundcube.nix
     ./zipline.nix
+    ./containerization.nix
   ];
 }