fix(etna): make shlink db persistent

systems/etna/shlink.nix

@@ -4,10 +4,10 @@
   virtualisation.oci-containers.containers.shlink = {
     image = "shlinkio/shlink:stable";
     ports = ["8081:8080"];
+    volumes = ["/data/shlink/database.sqlite:/etc/shlink/data/database.sqlite"];
     environment = {
       DEFAULT_DOMAIN = "uku.moe";
       IS_HTTPS_ENABLED = "true";
-      BASE_PATH = "/s";
     };
   };
 }