Add recurring expense functionality

[trandall2]

What

• Closes issue Recurring expenses #5
  • An expense can be created with a recurrence/repeating rule, and subsequent expenses will be created
  • Deleting the most recent expense causes no further repeating expenses to be created
  • Changing the most recent expense to no longer repeat causes no further repeating expenses to be created
  • Changing the recurrence rule of the most recent expense causes all subsequent expenses to adopt the same recurrence

Particular shortcomings to note

• Creating a monthly expense on the 29th, 30th, or 31st will not cause the expense to consistently be created for that date
  • If an expense is created on any of these 3 dates, it will eventually adopt the largest date available in the next month if the target date is not available
  • Ex 1
    • A monthly expense is initially created on January 31st, 2024
    • The next 3 expenses will be created on: February 29th, March 29th, and April 29th
  • Ex 2
    • A monthly expense is initially created on March 31st, 2024
    • The next 3 expenses will be created on: April 30th, May 30th, and June 30th
  • Ex 3
    • A monthly expense is initially created on July 31st, 2024
    • The next 3 expenses will be created on: August 31st, September 30th, and October 30th

Acknowledged decisions

• Only supporting recurrence rules (daily, weekly, and "monthly" -- excluding the 29th, 30th, and 31st)
  • This seems like a good starting place for the feature
• Not indefinitely linking Expenses to their future related Expenses
  • It's still an option to add this linking later. But not adding it now keeps the model more flexible
• Creating repeating Expenses when a user loads all the Expenses from a group
  • I took inspiration from this earlier PR which chose to do something similar. I think that it's possible/straightforward to add a job to perform this task. But this method was very lightweight and doesn't preclude a later change.

Potential Future improvements

• Add usage of the rrule library to hopefully avoid the poor end-of-month recurrence behavior mentioned above
  • I think it would be best to add this library before adding more RecurrenceRules (ex. bi-weekly, etc)
• Add a popup to the Expense page that notifies users about particular deletion behavior:
  • If they are deleting an Expense whose RecurringExpenseLink is pending to create the next Expense, then no further repeating Expenses will be created for that Expense
  • If they are deleting an Expense whose RecurringExpenseLink has already created the next Expense, then only the target Expense will be deleted

[trandall2]

Test feature in action:

[trandall2]

[Maxco10]

@trandall2 You should add the new labels for all languages not only for es-US.

[tasken]

Adding spanish translation strings

[tasken]

Recurrencia del gasto

[trandall2]

Added translations