feat(etna): add postgresql backups

systems/etna/postgresql.nix

@@ -0,0 +1,19 @@
+{ pkgs, ... }:
+{
+  services = {
+    postgresql = {
+      enable = true;
+      package = pkgs.postgresql_16;
+
+      port = 5432;
+      enableTCPIP = true;
+    };
+
+    postgresqlBackup = {
+      enable = true;
+      backupAll = true;
+      compression = "zstd";
+      location = "/data/backups/postgresql";
+    };
+  };
+}