support for subdirectories

[ajgon]

This PR adds support for flake.nix files not stored in the root of the repository.

I'm aware, that my use-case may be a little bit extra-ordinary, but I maintain one big, gitops monorepo with bunch of stuff separated in different subdirectories (i.e. k8s manifests in k8s, nix flakes in nix etc.). This PR will add support of such cases, by providing option to set up custom subdirectory, while still maintaing compatibility (as the param defaults to ".").

I also tested this branch on my local machine, and no issues so far.

[nlewo]

Hello @ajgon!

I agree on the principle but i think the proposed option name could be confusing with the url of the repository (remotes.*.url).

What about flakeSubdirectory (or flakeRelativeDirectory)?

This is the description of this option in the Nix manual:

dir: The subdirectory of the flake in which flake.nix is located. This parameter enables having multiple flakes in a repository or tarball. The default is the root directory of the flake.

(We could also have added this option in remotes.*.flakeSubdirectory but the proposed implementation looks good to me.)

[ajgon]

I agree, repo_dir wasn't a very good name :) I renamed it to flake_subdirectory as suggested, which sounds way better.

Regarding adding this options to remotes.* - I'm not sure if this is a good idea. From what I understood from the code, multiple remotes are generally the same git repository on different locations and is/are cloned to the same directory. Meaning the directory structure remain the same (i.e. they are equivalent of git remote add .....), so this option there wouldn't make much sense (as it has to be the same on each)?

[nlewo]

Thanks for the changes.

One last thing: option names should be camelCase in NixOS modules.
Could you rename flake_subdirectory to flakeSubdirectory in the NixOS module?

(Regarding current option names ( such as auth_token_path), I did some mistakes and i plan to rename them.)

[nlewo]

Thank you for your contribution.