Add template_ext to BigQueryInsertJobOperator (#9568)

airflow/providers/google/cloud/operators/bigquery.py

@@ -1664,6 +1664,7 @@ class BigQueryInsertJobOperator(BaseOperator):
     """
 
     template_fields = ("configuration", "job_id")
+    template_ext = (".json", )
     ui_color = BigQueryUIColors.QUERY.value
 
     def __init__(
@@ -1685,6 +1686,12 @@ class BigQueryInsertJobOperator(BaseOperator):
         self.gcp_conn_id = gcp_conn_id
         self.delegate_to = delegate_to
 
+    def prepare_template(self) -> None:
+        # If .json is passed then we have to read the file
+        if isinstance(self.configuration, str) and self.configuration.endswith('.json'):
+            with open(self.configuration, 'r') as file:
+                self.configuration = json.loads(file.read())
+
     def execute(self, context: Any):
         hook = BigQueryHook(
             gcp_conn_id=self.gcp_conn_id,