add support for optional arguments

Author: parthea

.generator/cli.py

@@ -289,6 +289,9 @@ def handle_generate(
                                 generator_options.append(
                                     f"{config_key_map[key]}={config_value},"
                                 )
+                    optional_arguments = result[py_gapic_entry].get("opt_args", None)
+                    if optional_arguments:
+                        [generator_options.append(f"{opt_arg},") for opt_arg in optional_arguments]
                     with tempfile.TemporaryDirectory() as tmp_dir:
                         generator_command = (
                             f"protoc {api_path}/*.proto --python_gapic_out={tmp_dir}"