Add release.nix to build skeleton with all targets

- release.nix builds the skeleton's serverExe and containerImage for
  both wasm and js targets via linkFarm, so `nix-build release.nix`
  builds everything in one go.
- Expose config and nixpkgs on project output so downstream consumers
  (like release.nix) can access the evaluated module config and the
  nixpkgs instance without re-importing.
- Add release to flake.nix packages (nix build .#release).

Author: ymeister

flake.nix

@@ -10,7 +10,9 @@
       );
 
       packages = eachSystem (system:
-        import ./nix/docs.nix { inherit system; }
+        (import ./nix/docs.nix { inherit system; }) // {
+          release = import ./release.nix { inherit system; };
+        }
       );
     };
 

nix/default.nix

@@ -24,6 +24,9 @@ in lib // {
           js = lib.mkServerExe { inherit proj; target = "js"; };
         };
     in proj // {
+      config = eval.config;
+      nixpkgs = eval.nixpkgs;
+
       exe = {
         wasm = (proj.override { obelisk.frontend.target = "wasm"; }).hsPkgs.backend.components.exes.backend;
         js = (proj.override { obelisk.frontend.target = "js"; }).hsPkgs.backend.components.exes.backend;

release.nix

@@ -0,0 +1,10 @@
+{ system ? builtins.currentSystem }:
+
+let skeleton = import ./skeleton { inherit system; };
+
+in skeleton.nixpkgs.linkFarm "obelisk-release" [
+  { name = "serverExe-wasm"; path = skeleton.serverExe.wasm; }
+  { name = "serverExe-js"; path = skeleton.serverExe.js; }
+  { name = "containerImage-wasm"; path = skeleton.containerImage.wasm; }
+  { name = "containerImage-js"; path = skeleton.containerImage.js; }
+]