Added example for defaults in conn.extras (#35165)

Added example for providing a default value when reading extras from connections using extra_dejson.get

(cherry picked from commit 7c80b2b)

docs/apache-airflow/templates-ref.rst

@@ -136,6 +136,7 @@ Just like with ``var`` it's possible to fetch a connection by string  (e.g. ``{{
 
 Additionally, the ``extras`` field of a connection can be fetched as a Python Dictionary with the ``extra_dejson`` field, e.g.
 ``conn.my_aws_conn_id.extra_dejson.region_name`` would fetch ``region_name`` out of ``extras``.
+This way, defaults in ``extras`` can be provided as well (e.g. ``{{ conn.my_aws_conn_id.extra_dejson.get('region_name', 'Europe (Frankfurt)') }}``).
 
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