Inject the embedded image tag late

This allows us to make an image tarball that can be loaded with `podman
load` and end up with the expected tag.

Author: Ramblurr

flake.nix

@@ -23,13 +23,19 @@
       {
         overlays = final: prev: {
           datomic-pro = pkgs.callPackage ./pkgs/datomic-pro.nix { };
-          datomic-pro-container = pkgs.callPackage ./pkgs/datomic-pro-container-image.nix { };
+          datomic-pro-container = pkgs.callPackage ./pkgs/datomic-pro-container-image.nix {
+            imageTag = final.datomic-pro.version;
+          };
+          datomic-pro-container-unstable = pkgs.callPackage ./pkgs/datomic-pro-container-image.nix {
+            imageTag = "unstable";
+          };
           datomic-generate-properties = pkgs.callPackage ./pkgs/datomic-generate-properties.nix { };
         };
         packages = {
           default = self.packages.${system}.datomic-pro;
           datomic-pro = pkgs.datomic-pro;
           datomic-pro-container = pkgs.datomic-pro-container;
+          datomic-pro-container-unstable = pkgs.datomic-pro-container-unstable;
           datomic-generate-properties = pkgs.datomic-generate-properties;
         };
         nixosModules = {

pkgs/datomic-pro-container-image.nix

@@ -1,4 +1,5 @@
 {
+  imageTag,
   lib,
   stdenv,
   fetchzip,
@@ -45,7 +46,7 @@ let
 in
 dockerTools.buildLayeredImage {
   name = "ghcr.io/ramblurr/datomic-pro";
-  tag = datomic-pro.version;
+  tag = imageTag;
   fromImage = null;
   contents = [
     datomic-pro