nixos/phoebus: add modules

Add the possibility to enable phoebus in a nixos configuration
Add the possibility to edit java_opts

nixos/module-list.nix

@@ -5,6 +5,7 @@
   ./modules/channel-finder/service.nix
   ./modules/phoebus/alarm-logger.nix
   ./modules/phoebus/alarm-server.nix
+  ./modules/phoebus/client.nix
   ./modules/phoebus/olog.nix
   ./modules/phoebus/save-and-restore.nix
 ]

nixos/modules/phoebus/client.nix

@@ -0,0 +1,27 @@
+{
+  config,
+  lib,
+  epnix,
+  pkgs,
+  ...
+}: let
+  cfg = config.programs.phoebus-client;
+  pkg = pkgs.epnix.phoebus.override {java_opts = cfg.java_opts;};
+in {
+  options.programs.phoebus-client = {
+    enable = lib.mkEnableOption ''Enable the Phoebus client'';
+    java_opts = lib.mkOption {
+      type = lib.types.str;
+      default = "-XX:MinHeapSize=128m -XX:MaxHeapSize=4g -XX:InitialHeapSize=1g -XX:MaxHeapFreeRatio=10 -XX:MinHeapFreeRatio=5 -XX:-ShrinkHeapInSteps -XX:NativeMemoryTracking=detail";
+      example = "-XX:MinHeapSize=128m -XX:MaxHeapSize=4g -XX:InitialHeapSize=1g";
+      description = ''
+        This wrapper for the `phoebus-unwrapped` executable sets the `JAVA_OPTS`
+        environment variable with the provided `java_opts` value.
+      '';
+    };
+  };
+
+  config = lib.mkIf cfg.enable {
+    environment.systemPackages = [pkg];
+  };
+}