ofborg/src/maintainers.nix: look up files pointed by "pos" attribute

[trofi]

Sometimes most of attributes for a package are defined outside the file
that defines it. Examples are openjdk and nix.

At least openjdk defined pos attribute to guide nix edit to open
the right file. Let's extend ofborg to do the same.

Before the change (with pos applied to nix_2_3):

$ printf '[["nix_2_3"]]' > attrs.json; \
  printf '["pkgs/tools/package-management/nix/default.nix"]' > paths.json; \
  nix-instantiate --eval maintainers.nix --arg changedattrsjson ./attrs.json --arg changedpathsjson ./paths.json
{ }

After the change:

$ printf '[["nix_2_3"]]' > attrs.json; \
  printf '["pkgs/tools/package-management/nix/default.nix"]' > paths.json; \
  nix-instantiate --eval maintainers.nix --arg changedattrsjson ./attrs.json --arg changedpathsjson ./paths.json
{ flokli = <CODE>; raitobezarius = <CODE>; }

[trofi]

It should be nit pos of a pos but just pos. Converting to draft.

[trofi]

With NixOS/nixpkgs#276892 applied confirmed that nix_2_3 attribute change resolves maintainers as expected. Updated the comment description to include the test.

[Mindavi]

Is nixos/released intentionally the target branch?

[cole-h]

Is nixos/released intentionally the target branch?

Yes, released is the default branch for this repository.

[cole-h]

LGTM.