postgresql.withPackages: add dev output

This avoids leaking the dev output and all its dependencies into regular
postgresql.withPackages builds, most notably postgresql_jit.

pkgs/servers/sql/postgresql/generic.nix

@@ -641,7 +641,8 @@ let
     f:
     let
       installedExtensions = f postgresql.pkgs;
-      finalPackage = buildEnv {
+      finalPackage =
+        (buildEnv {
           name = "${postgresql.pname}-and-plugins-${postgresql.version}";
           paths = installedExtensions ++ [
             # consider keeping in-sync with `postBuild` below
@@ -666,8 +667,8 @@ let
             ''
               wrapProgram "$out/bin/postgres" ${lib.concatStringsSep " " args}
 
-            mkdir -p "$out/nix-support"
-            substitute "${lib.getDev postgresql}/nix-support/pg_config.env" "$out/nix-support/pg_config.env" \
+              mkdir -p "$dev/nix-support"
+              substitute "${lib.getDev postgresql}/nix-support/pg_config.env" "$dev/nix-support/pg_config.env" \
                 --replace-fail "${postgresql}" "$out" \
                 --replace-fail "${postgresql.man}" "$out"
             '';
@@ -710,6 +711,13 @@ let
                   ;
               } (ps: installedExtensions ++ f' ps);
           };
+        }).overrideAttrs
+          {
+            # buildEnv doesn't support passing `outputs`, so going via overrideAttrs.
+            outputs = [
+              "out"
+              "dev"
+            ];
           };
     in
     finalPackage;