refactor: pluralize endpoint names

[umar-ahmed]

Description

• It's more intuitive to pluralize endpoint names because some endpoints return more than one instance of the resource
• ex. /response implies a single resource is returned, when you actually get an array of responses

Checklist

• [ ] I have written unit tests for the code I added

QA Steps

1. npm run build
2. npm run dev:backend
3. npm run dev: frontend
4. Verify all endpoints in openapi are pluralized
5. Verify frontend still works correctly

[DiademShoukralla]

QA Steps

1. npm run build
2. npm run dev:backend
3. npm run dev: frontend
4. Verify all endpoints in openapi are pluralized ✔️
5. Verify frontend still works correctly ✔️
6. Very existing backend API endpoint tests still work ✔️ ((All API endpoints appear updated in the test file and the current working test is verified to be updated.)) QA Pass