feat: Add pack_samples junction table for many-to-many relationships

Commit notes

- Introduced a new SQL migration to create the "pack_samples" junction table, enabling samples to be associated with multiple packs. - Added unique constraints and indexes for efficient querying of sample-pack relationships. - Updated existing sample-pack relationships to migrate data into the new junction table. - Modified relevant database schema and relations to accommodate the new many-to-many structure. - Adjusted various routes and services to utilize the junction table for sample management and retrieval.