Define and implement GET /finance/budgets/id/expense-classes-totals API

Purpose/Overview:
Provide API to retrieve collection of expense classes with totals within a given Budget.

Requirements/Scope:

1. create schema budget_expense_class_totals
   • expenseClassName
   • expenseClassStatus
   • encumbered
   • awaitingPayment
   • expended
   • percentageExpended

• define and implement GET /finance/budgets/id/expense-classes API

Approach:
Retrieve expense-classes for given budget using GET /finance-storage/expense-classes?query=budgetExpenseClass.budgetId==id
For each expense-class get transactions using GET /finance-storage/transactions?query=expenseClassId==expense-class.id AND fundId=budget.fundId AND fiscalYearId=budget.fiscalYearId
Calculate for each expense-class:

• encumbered sum of transaction.amount where transactionType==Encumbrance
• awaitingPayment sum of transaction.amount where transactionType==Pending payment
• expended sum of (transaction.amount where transactionType==Payment) and (-transaction.amount where transactionType==Credit)
• percentageExpended = expended / (budget.expended+ budget.overExpened) * 100

Acceptance criteria:

• schema created
• GET /finance/groups/id/expense-classes API defined and implemented
• unit tests updated
• API tests updated