[DEV-11209] create spending-by-category/defc endpoint

[ronaldongbah]

Description:

A new endpoint added called spending_by_category/defc in order to support the Top 5 section in the State Profile Page as well as the Advanced Search Spending by Category section.

Technical details: The technical details for the knowledge of other developers. Any detailed caveats or specific deployment steps should be outlined here.

Requirements for PR merge:

1. [ ] Unit & integration tests updated
2. [ ] API documentation updated
3. [ ] Necessary PR reviewers:
   • [ ] Backend
   • [ ] Frontend <OPTIONAL>
4. [ ] Matview impact assessment completed
5. [ ] Frontend impact assessment completed
6. [ ] Data validation completed
7. [ ] Appropriate Operations ticket(s) created
8. [x] Jira Ticket DEV-11209:
   • [ ] Link to this Pull-Request

Area for explaining above N/A when needed: