feat(submodules): add support for submodule exports

tests/submodules/exports.nix

@@ -0,0 +1,32 @@
+{ name, config, lib, kubenix, subm-lib, ... }:
+
+with lib;
+
+let
+  submodule = {
+    imports = [ kubenix.modules.submodule ];
+
+    config.submodule = {
+      name = "subm";
+      exports = {
+        inherit id;
+      };
+    };
+  };
+in {
+  imports = with kubenix.modules; [ test submodules ];
+
+  test = {
+    name = "submodules-exports";
+    description = "Submodules exports test";
+    assertions = [{
+      message = "should have library exported";
+      assertion = subm-lib.id 1 == 1;
+    }];
+  };
+
+  submodules.imports = [{
+    modules = [submodule];
+    exportAs = "subm-lib";
+  }];
+}