feat: add gidMap option to containerConfig

GIDMap allows for more advanced group configurations than userNS can do.
Useful for solving permission issues with containers that arent built to
run with rootless operation in mind.

container.nix

@@ -142,6 +142,14 @@ let
       description = "--user UID:...";
       property = "Group";
     };
+
+    gidMap = quadletUtils.mkOption {
+      type = types.nullOr types.str;
+      default = null;
+      example = "0:10000:10";
+      description = "--gidmap";
+      property = "GIDMap";
+    };
 
     healthCmd = quadletUtils.mkOption {
       type = types.nullOr types.str;