Add `KubernetesPodOperat` `pod-template-file` jinja template support (#15942)

This PR adds jinja template support for KubernetesPodOperator
pod-template-file.

fixes #15892
diff --git a/airflow/providers/cncf/kubernetes/operators/kubernetes_pod.py b/airflow/providers/cncf/kubernetes/operators/kubernetes_pod.py
index bf0cf81..15c83df 100644
--- a/airflow/providers/cncf/kubernetes/operators/kubernetes_pod.py
+++ b/airflow/providers/cncf/kubernetes/operators/kubernetes_pod.py
@@ -172,6 +172,8 @@
         'pod_template_file',
     )
 
+    template_ext = ('yaml', 'yml', 'json')
+
     # fmt: off
     def __init__(  # pylint: disable=too-many-arguments,too-many-locals
         # fmt: on