dockerTools.buildLayeredImage: image names with registry/ prefix

When using `buildLayeredImage`, it is not possible to specify an image
name of the form `<registry>/my/image`, although it is a valid name.

This is due to derivations under `buildLayeredImage` using that image
name as their derivation name, but slashes are not permitted in that
context.

A while ago, #13099 fixed that exact same problem in `buildImage` by
using `baseNameOf name` in derivation names instead of `name`. This
change does the same thing for `buildLayeredImage`.

pkgs/build-support/docker/examples.nix

@@ -427,4 +427,18 @@ rec {
       tag = "latest";
       contents = [ pkgs.bash symlink ];
     } // { passthru = { inherit symlink; }; };
+
+  # image with registry/ prefix
+  prefixedImage = pkgs.dockerTools.buildImage {
+    name = "registry-1.docker.io/image";
+    tag = "latest";
+    config.Cmd = [ "${pkgs.hello}/bin/hello" ];
+  };
+
+  # layered image with registry/ prefix
+  prefixedLayeredImage = pkgs.dockerTools.buildLayeredImage {
+    name = "registry-1.docker.io/layered-image";
+    tag = "latest";
+    config.Cmd = [ "${pkgs.hello}/bin/hello" ];
+  };
 }