Send JSON error instead of entire 500 page error on autograde error

[michellexliu]

Description

When there's an error in the partial feedback request a json { error: "Get partial feedback request failed: #{e}" } with status internal_server_error gets rendered instead of a full 500 error page.

Motivation and Context

Previously, if there's an autograding error, the error gets properly caught in the javascript of viewFeedback and functionally everything was fine, but the error response that gets sent is the HTML for the entire donkey 500 error page, which makes the response slower. This PR will return a simpler JSON.

Error response before:

Error response after:

How Has This Been Tested?

• Same tests from Autolab partial feedback endpoints #1645
• Trigger error in Tango --> make sure it's caught properly & responds w/ error json instead of full 500 error HTML

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• I have run rubocop for style check. If you haven't, run overcommit --install && overcommit --sign to use pre-commit hook for linting
• My change requires a change to the documentation, which is located at Autolab Docs
• I have updated the documentation accordingly, included in this PR

[victorhuangwq]

LGTM