Modify the agent to use the new configuration endpoints

# Refactor

## Component(s) to be refactored

- Agent

## Explanation
Use the new configuration endpoints introduced in #2000 in the agent.

## Tasks
- [x] Modify `ControlChannel` to use the new endpoint (0d) @ilija-lazoroski 
- [x] Remove `GET /api/agent` endpoint (0d) @ilija-lazoroski 