Refactor relationships in AssignedOrders and Stock models

[NourAlPha]

This pull request updates the entity relationships in the AssignedOrders and Stock models to improve database consistency and better reflect the intended data structure. The changes include renaming a mapped field, introducing a new relationship, and modifying an existing join column.

Changes to entity relationships:

• AssignedOrders model:

  • Updated the mapping of the items field to use assignedOrder instead of packagedOrder in the Stock entity. ([src/main/java/com/podzilla/warehouse/Models/AssignedOrders.javaL36-R36](https://github.com/Podzilla/warehouse/pull/58/files#diff-0903df3387465c62f90f237168b13fcec88a43dea606a450e13b29c9649bbd51L36-R36))

• Stock model:

  • Added a new @ManyToOne relationship to the AssignedOrders entity, with a join column named assigned_order_id and a nullable constraint. This introduces a reverse mapping to AssignedOrders. ([src/main/java/com/podzilla/warehouse/Models/Stock.javaR37-R44](https://github.com/Podzilla/warehouse/pull/58/files#diff-2e58d935c5017aa420bf97eefc92901538aa4fa2e972844fe5f1c118ad7686b1R37-R44))
  • Renamed the join column for the existing packagedOrder relationship to packaged_order_id for clarity and consistency. ([src/main/java/com/podzilla/warehouse/Models/Stock.javaR37-R44](https://github.com/Podzilla/warehouse/pull/58/files#diff-2e58d935c5017aa420bf97eefc92901538aa4fa2e972844fe5f1c118ad7686b1R37-R44))