Refactor GetPublicPacks and GetPackByCreatorAndSlug handlers for improved access control

Commit notes

- Removed the attachment of download URLs for public catalog samples when the user has purchased the pack. - Enhanced purchase status check to include pack creators, allowing them access to their own packs. - Updated preview URL generation to use a token-based approach for better security. - Streamlined the handling of authorization tokens for download URLs, ensuring proper access management.