Handle rendering errors from reStructuredText

What does this MR do and why?

Contributes to #385712 (closed)

Sentry error: https://new-sentry.gitlab.net/organizations/gitlab/issues/1594

Problem

Unlike other renderers 'reStructuredText' can raise an exception if the context does not follow the required structure.

Solution

Use a simpler renderer instead of raising 500 error.

Screenshots or screen recordings

Before	After

How to set up and validate locally

1. Create file test.rst with invalid content

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PART
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2. Try to open this file

MR acceptance checklist

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• I have evaluated the MR acceptance checklist for this MR.