[DEV-11399] Add outlays to Spending over time and separate Awards and Transactions data sources

[aguest-kc]

Description: Add outlays to the response of the /spending_over_time endpoint. Add a new spending_level filter field that specifies which data source to use. Use the AwardSearch Elasticsearch index when the spending_level is awards instead of the TransactionSearch index.

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. [x] Unit & integration tests updated
2. [x] API documentation updated
3. [x] Necessary PR reviewers:
   • [x] Backend
   • [x] Frontend
4. [x] Frontend impact assessment completed
5. [x] Data validation completed
6. [ ] Appropriate Operations ticket(s) created
7. [x] Jira Ticket DEV-11399:
   • [x] Link to this Pull-Request

Area for explaining above N/A when needed:

4. Matview impact assessment completed
No matviews are affected by this change.