[DEV-11405]: Updating API Endpoint Logic

[LKambhampati-frb]

Description: DEV-10991: Updates to Spending by Subagency Endpoints made updates to two Spending by Subagency Endpoints. After implementation, it was discovered that the updates did not fully meet the frontend needs, so some additional changes are necessary.

Requirements for PR merge:

1. [x] Unit & integration tests updated
2. [x] API documentation updated
3. [x] Necessary PR reviewers:
   • [ ] Backend
   • [x] Frontend <OPTIONAL> (N/A)
   • [x] Operations <OPTIONAL> (N/A)
   • [x] Domain Expert <OPTIONAL> (N/A)
4. [x] Matview impact assessment completed (N/A)
5. [x] Frontend impact assessment completed (N/A)
6. [x] Data validation completed
7. [x] Appropriate Operations ticket(s) created
8. [x] Jira Ticket DEV-11405:
   • [x] Link to this Pull-Request
   • [x] Performance evaluation of affected (API | Script | Download)
   • [x] Before / After data comparison

Area for explaining above N/A when needed: 3b, 3c, 3d The nature of this work does not require PR reviews from these groups 4. The nature of this work does not impact materialized views 5. The nature of this work does not require an impact assessment from the frontend