[nix] Modularized the container backend so I can easily switch it with an option

system/hosts/mcp/containers/gitea.nix

@@ -1,14 +1,14 @@
 { config, ... }:
-let 
+let
   inherit (import ./lib.nix config) mkContainer blazestar;
 in
 {
   sops.secrets = {
     "gitea/db_password" = {
-      restartUnits = [ "podman-gitea.service" ];
+      restartUnits = [ "${config.local.container-backend}-gitea.service" ];
     };
     "gitea/registration_token" = {
-      restartUnits = [ "podman-gitea-runner.service" ];
+      restartUnits = [ "${config.local.container-backend}-gitea-runner.service" ];
     };
   };
 
@@ -66,7 +66,7 @@ in
     ];
     volumes = [
       # The runner will spawn new containers to run the actions
-      "/var/run/podman/podman.sock:/var/run/docker.sock:ro"
+      "${config.local.container-socket}:/var/run/docker.sock:ro"
     ];
   };
 }