feat(grafana): add providers configuration

[alexpearce]

Addresses #210.

I've tested this by hand with configuration:

services.grafana."grafana" = {
  enable = true;
  providers = [
    {
      name = "Databases";
      type = "file";
      options = {
        path = ./dashboards;
        foldersFromFilesStructure = true;
      };
    }
  ];
};

I haven't looked into it, but it might be possible to extend the existing Grafana test to check that a folder of dashboards is loaded.

[shivaraj-bh]

It would be nice to also see a test for this option!

[alexpearce]

I'm not sure how best to run the tests locally. test/flake.nix refers services-flake as juspay/services-flake so it won't pick up changes in my local repo.

[shivaraj-bh]

I'm not sure how best to run the tests locally. test/flake.nix refers services-flake as juspay/services-flake so it won't pick up changes in my local repo.

Once in the devShell you can run just test grafana to run the test locally

[alexpearce]

Nice, thanks!

I had to modify the tests to use nixos-24.05 to work around the Grafana-on-macOS issue, but with my latest commit the tests pass.

[shivaraj-bh]

Thanks @alexpearce