Add searchpath to TemplateNotFound exception message

[tirkarthi]

This was from apache/airflow#23333 where trying to load a template that doesn't exist in the searchpath raises TemplateNotFound exception. In this case an absolute path is used which causes issue over concatenation but including searchpath might be a useful addition so that user can know under the paths under which the template was searched for and will be helpful during debugging.

jinja/src/jinja2/loaders.py

Line 218 in 6f79daa

raise TemplateNotFound(template)

Current exception :

jinja2.exceptions.TemplateNotFound: /tmp/a/python_template_exts.txt

Proposed exception to include searchpath :

jinja2.exceptions.TemplateNotFound: /tmp/a/python_template_exts.txt not found in search path ['/opt/airflow/tests/operators', '/']