ildkule: add config for prometheus_mysqld_exporter

There's a PR waiting to add this module to nixpkgs,
so we should enable this once it gets merged.

hosts/ildkule/services/metrics/prometheus/mysqld.nix

@@ -0,0 +1,25 @@
+{ config, unstable, ... }: let
+  cfg = config.services.prometheus;
+in {
+  sops.secrets."config/mysqld_exporter" = { };
+
+  services.prometheus = {
+    scrapeConfigs = [{
+      job_name = "mysql";
+      scheme = "http";
+      metrics_path = cfg.exporters.mysqld.telemetryPath;
+      static_configs = [
+        {
+          targets = [
+            "localhost:${toString cfg.exporters.mysqld.port}"
+          ];
+        }
+      ];
+    }];
+
+    exporters.mysqld = {
+      enable = true;
+      configFilePath = config.sops.secrets."config/mysqld_exporter".path;
+    };
+  };
+}