clarify process_template_response API works with duck-typed TemplateResponse
|Reported by:||ptone||Owned by:||ptone|
|Has patch:||yes||Needs documentation:||no|
|Needs tests:||no||Patch needs improvement:||no|
The API for the template response middleware was documented in a way that implied only a subclass of SimpleTemplateResponse was acceptable as the response object, but in fact duck typing is specifically and deliberately employed.