Improve the display of route-based warning messages, particularly in the user guide

[toph-allen]

Right now, when type annotations are insufficient for us to generate Tableau usage examples, we display a warning message in its place.

We could instead pass this data up to the RouteInfo object and use this to alter the display of the function in the user guide, to provide a more distinct and informative warning message.

This would also be a good place to surface warnings about endpoints that do not meet Tableau criteria (i.e. with too-complex Pydantic models). We could display a warning message at the top of the landing page to the effect of "Some endpoints will not work with Tableau. Click here [link to user guide] to see more." In the user guide, we could display more informative message about endpoints that won't work.