nixos/telegraf: include procps if procstat input is configured

nixos/modules/services/monitoring/telegraf.nix

···
 
   ###### implementation
   config = mkIf config.services.telegraf.enable {
+    services.telegraf.extraConfig = {
+      inputs = {};
+      outputs = {};
+    };
     systemd.services.telegraf = let
       finalConfigFile = if config.services.telegraf.environmentFiles == []
                         then configFile
···
       description = "Telegraf Agent";
       wantedBy = [ "multi-user.target" ];
       after = [ "network-online.target" ];
+      path = lib.optional (config.services.telegraf.extraConfig.inputs ? procstat) pkgs.procps;
       serviceConfig = {
         EnvironmentFile = config.services.telegraf.environmentFiles;
         ExecStartPre = lib.optional (config.services.telegraf.environmentFiles != [])

nixos/tests/telegraf.nix

···
     services.telegraf.extraConfig = {
       agent.interval = "1s";
       agent.flush_interval = "1s";
+      inputs.procstat = {};
       inputs.exec = {
         commands = [
           "${pkgs.runtimeShell} -c 'echo $SECRET,tag=a i=42i'"