feat: add an option to cabal2nix hook for specifying output filename.

[rsrohitsingh682]

At present after enabling cabal2nix hook, it generates a file named default.nix which is hardcoded. It is better if user has an option to specify the filename instead of using hardcoded default.nix.

This PR adds an option to cabal2nix hook to specify output filename generated by running cabal2nix.

Example:

cabal2nix = {
   enable = true;
   settings.output_filename = "cabal.nix";
};

[rsrohitsingh682]

@sandydoo @NorfairKing Any thoughts on this PR ?

[NorfairKing]

I don't see a use case so think this needlessly complicating things but I also don't really care 🤷

[rsrohitsingh682]

I don't see a use case so think this needlessly complicating things but I also don't really care 🤷

It's required for me as I don't want pre-commit hook to generate a default.nix. Anyways since the default is default.nix so the default behaviour still remains the same.

[rsrohitsingh682]

@sandydoo Could you please help with the review ?

[sandydoo]

Otherwise, LGTM

[sandydoo]

The CI failure is unrelated. This branch needs a rebase on master.