Exceptions are unhandled when rendering a config template via the REST API

[jeremystretch]

NetBox version

v3.5-beta1

Python version

3.8

Steps to Reproduce

1. Create a config template with the following code:

{{ foo|bar }}

2. Assign the config template to a device
3. Attempt to render the device's configuration by making a REST API call to the /api/dcim/devices/<id>/render-config/ endpoint

Expected Behavior

Rendering should fail and return an error message indicating the reason. (The template filter bar is invalid.)

Observed Behavior

A TemplateAssertionError exception is raised and not handled.