Return content from repo in snippet raw endpoint

What does this MR do?

Before this MR, the raw endpoint in both project and personal snippets were returning the snippet content from the database, but that is no longer true.

If the feature flag version_snippets is enabled and the snippet repository is not empty we must return the content from the repository.

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content