Resolve "Change incorrect Entity in Snippet API"

What does this MR do?

Updates the Snippet API for GET /snippets to use Entities::Snippet instead of Entities::PersonalSnippet.

The endpoint returns both Personal and Project Snippets, so this entity is incorrect.

Blocked by !29776 (merged) which will move the raw_url to the base entity.

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.

Relates #215012 (closed)