Add fiscalYear query arg to GET /finance/ledgers API

Overview

The basic implementation of GET /finance/ledgers exists, but needs to be augmented to support the ability to get the summary values (available, unavailable, allocated) for the ledgers.

This involves adding an optional query argument "fiscalYear" as well as business logic as described on the wiki

Acceptance Criteria

• A fiscal year can be specified when calling GET /finance/ledgers and the results will be populated with appropriate summary data
• Unit tests are updated
• API tests are updated