nixos/promtail: configFile for passing path as config

[Kek5chen]

Description of changes

Added an option that is used instead of the configurations attribute in case you wish to use a config file instead.

Shouldn't break existing configurations.

Things done

• Built on platform(s)

  • x86_64-linux
  • aarch64-linux
  • x86_64-darwin
  • aarch64-darwin

• Tested, as applicable:

  • NixOS test(s) (look inside nixos/tests)
  • and/or package tests
  • or, for functions and "core" functionality, tests in lib/tests or pkgs/test
  • made sure NixOS tests are linked to the relevant packages

• Tested compilation of all packages that depend on this change using nix-shell -p nixpkgs-review --run "nixpkgs-review rev HEAD". Note: all changes have to be committed, also see nixpkgs-review usage

• Tested basic functionality of all binary files (usually in ./result/bin/)

• 24.11 Release Notes (or backporting 23.11 and 24.05 Release notes)

  • (Package updates) Added a release notes entry if the change is major or breaking
  • (Module updates) Added a release notes entry if the change is significant
  • (Module addition) Added a release notes entry if adding a new NixOS module

• Fits CONTRIBUTING.md.

[FliegendeWurst]

I think it would be good to mention that configFile and configuration are incompatible options

[FliegendeWurst]

LGTM. Please squash your commits

[Kek5chen]

@FliegendeWurst done ":3

[NetaliDev]

I've also tested it, and it works as it should.