Add 'flakes' to extra experimental features

[the-furry-hubofeverything]

In my flake setup, I use flake: for my nixPaths because I wanted compatibility with legacy commands. However, this didn't work well with nurl when I was using it -

[hubble@Gulo-Laptop:/run/media/hubble/Data/GithubFurry/nixpkgs/pkgs/applications/misc/blender]$ nurl --fetcher fetchFromGitea https://projects.blender.org/blender/blender-addons v3.6.5 --arg-str postFetch 'patch -p3 -d $out < ${./draco-p2.patch}'
$ nix build --experimental-features nix-command --impure --no-link --expr '(import(<nixpkgs>){}).fetchFromGitea{domain="projects.blender.org";owner="blender";repo="blender-addons";rev="v3.6.5";hash="sha256-AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA=";postFetch="patch -p3 -d $out < ${./draco-p2.patch}";}'
Error: failed to find the hash from error messages
stdout: 
stderr:
error:
       … while calling the 'import' builtin

         at «string»:1:2:

            1| (import(<nixpkgs>){}).fetchFromGitea{domain="projects.blender.org";owner="blender";repo="blender-addons";rev="v3.6.5";hash="sha256-AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA=";postFetch="patch -p3 -d $out < ${./draco-p2.patch}";}
             |  ^

       … while calling the 'findFile' builtin

         at «string»:1:9:

            1| (import(<nixpkgs>){}).fetchFromGitea{domain="projects.blender.org";owner="blender";repo="blender-addons";rev="v3.6.5";hash="sha256-AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA=";postFetch="patch -p3 -d $out < ${./draco-p2.patch}";}
             |         ^

       error: experimental Nix feature 'flakes' is disabled; use '--extra-experimental-features flakes' to override

... particularly in for fod_prefetch.

With this PR:

[hubble@Gulo-Laptop:/run/media/hubble/Data/GithubFurry/nixpkgs/pkgs/applications/misc/blender]$ nurl --fetcher fetchFromGitea https://projects.blender.org/blender/blender-addons v3.6.5 --arg-str postFetch 'patch -p3 -d $out < ${./draco-p2.patch}'
$ nix build --extra-experimental-features 'nix-command flakes' --impure --no-link --expr '(import(<nixpkgs>){}).fetchFromGitea{domain="projects.blender.org";owner="blender";repo="blender-addons";rev="v3.6.5";hash="sha256-AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA=";postFetch="patch -p3 -d $out < ${./draco-p2.patch}";}'
fetchFromGitea {
  domain = "projects.blender.org";
  owner = "blender";
  repo = "blender-addons";
  rev = "v3.6.5";
  hash = "sha256-K4jbWuWaXtSjEqbmZC+7SnsNUJCcru1U1HuI4LCuuGM=";
  postFetch = "patch -p3 -d $out < ${./draco-p2.patch}";
}

Let me know if this is an acceptable solution for this problem