Rename, refactor, hide build.imagesToLoad

imagesToLoad is not the right api for non-service images.

src/nix/modules/composition/images.nix

@@ -28,6 +28,7 @@ in
   options = {
     build.imagesToLoad = lib.mkOption {
       type = listOf unspecified;
+      internal = true;
       description = "List of dockerTools image derivations.";
     };
   };

src/nix/modules/composition/service-info.nix

@@ -5,17 +5,14 @@
  */
 { config, lib, ... }:
 let
+  inherit (lib) mapAttrs filterAttrs;
+
   serviceInfo =
-    lib.mapAttrs getInfo (
-      lib.filterAttrs filterFunction config.services
+    filterAttrs (_k: v: v != {})
+      (mapAttrs (_serviceName: service: service.out.extendedInfo)
+        config.services
       );
 
-  filterFunction = _serviceName: service:
-    # shallow equality suffices for emptiness test
-    builtins.attrNames service.build.extendedInfo != [];
-
-  getInfo = _serviceName: service: service.build.extendedInfo;
-
 in
 {
   config = {

src/nix/modules/service/default-exec.nix

@@ -14,6 +14,6 @@ in
     };
   };
   config = {
-    build.extendedInfo.defaultExec = config.service.defaultExec;
+    out.extendedInfo.defaultExec = config.service.defaultExec;
   };
 }

src/nix/modules/service/extended-info.nix

@@ -4,8 +4,11 @@ let
   inherit (lib.types) attrsOf unspecified;
 in
 {
+  imports = [
+    (lib.mkRenamedOptionModule ["build" "extendedInfo"] ["out" "extendedInfo"])
+  ];
   options = {
-    build.extendedInfo = mkOption {
+    out.extendedInfo = mkOption {
       type = attrsOf unspecified;
       description = ''
         Information about a service to include in the Docker Compose file,