Resolve "Ensure project snippet feature status in project API endpoints"

What does this MR do?

Modifies ProjectSnippet API endpoints to check for feature status before doing any further snippet querying and return a 404 if they are disabled, as described in #37320 (closed)

This should increase API performance by removing unnecessary SnippetsFinder usage.

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation ([if required](https://docs.gitlab.com/ee/development/documentation/workflow.html#when-documentation-is-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.
• Tested in all supported browsers
• Informed Infrastructure department of a default or new setting change, if applicable per definition of done