[Draft][BackEnd] Create a "Savings Goals" feature

[FelipePSoares]

Users often want to set aside money for future expenses, such as investments, planned trips, or other long-term goals. This is not an immediate expense but a reserved amount that will be spent in the future. To support this functionality in the system, we need to identify and track these funds separately from regular income and expenses.

Requirements:

1. Model Changes

   • Create a new model: Save (inherits from BaseFinancial), which will represent individual savings entries towards a specific goal or reserve.

2. Category Updates

   • Add the following properties to the Category entity:
     • SavingGoal (boolean): Indicates if this category is a savings goal.
     • TargetAmount (decimal, optional): The target amount for this savings goal.
     • TargetDate (DateTime, optional): The target date by which the savings goal should be reached.
     • Savings (ICollection, optional): A collection of savings entries related to this category.
     • Spent (boolean): Marks if the savings goal has been spent or completed.

3. Behavior

   • Implement the full CRUD operations for savings on the back-end, allowing users to create, view, update, and delete savings goals and their associated savings entries.
   • If a savings goal (category) is canceled by the user, all associated Savings entries should also be canceled or deleted

Additional Considerations:

• Consider adding validation or business rules to prevent negative savings amounts or dates that have already passed.