use just busybox for image

flake.nix

@@ -32,16 +32,12 @@
         };
         dockerImage = pkgs.dockerTools.buildImage {
           name = "policy_service";
-          fromImageName = "hexpm/elixir";
+          contents = [
-          fromImageTag = "1.17.5-erlang-27.0-debian-bookworm-20240612";
+            package
-          copyToRoot = pkgs.buildEnv {
+            pkgs.busybox
-            name = "policy-service";
+          ];
-            paths = [ package ];
-            pathsToLink = [ "/bin" ];
-          };
           config = {
-            Cmd = [ "/bin/bash" ];
+            Cmd = [ "${package}/bin/policy_service" "start" ];
-            WorkingDir = "/";
           };
         };
       in