Resolve "Snippet file names in dashboard index"

What does this MR do?

As proposed in #213968 (closed), this MR changes the index view snippet partial to conditionally (depending on Feature flag status) lookup the the correct file name for a Snippet like we do here so that it can render the name like we do in the show view.

This means that if a user has the version_snippets FF enabled, their snippets will display the correct filename from the repo rather than the DB.

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.
• [-] Tested in all supported browsers
• [-] Informed Infrastructure department of a default or new setting change, if applicable per definition of done

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• [-] Label as security and @ mention @gitlab-com/gl-security/appsec
• [-] The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• [-] Security reports checked/validated by a reviewer from the AppSec team