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

Purpose/Overview:
To support ability to summarize the amounts associated with an expense class for all funds in given group with that type we need to provide GET /finance/groups/id/expense-classes-totals API

Requirements/Scope:

1. create schema group_expense_class_totals
   • expenseClassName
   • expended
   • percentageExpended
2. define and implement GET /finance/groups/id/expense-classes-totals API

Approach:
Retrieve group-fund-fiscal-year records by groupId
Retrieve expense-classes for each budgetId from above request 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
Calculate for each expense-class:

• expended sum of (transaction.amount where transactionType==Payment) and (-transaction.amount where transactionType==Credit)
• percentageExpended = expended/ (sum of all expense classes expended related to given group) * 100

Acceptance criteria:

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