- Added transaction support in `add_upstream_target`, `remove_upstream`, `remove_upstream_target`, `update_upstream`, and `update_upstream_target` functions to ensure atomicity of operations.
- Updated the `NginxService` to include methods for validating and applying configurations using the agent service.
- Enhanced error handling in agent service interactions, returning appropriate internal server errors when agent communication fails.
- Introduced mock agent service for testing, allowing for simulation of agent interactions without actual network calls.
- Refactored tests to cover scenarios where agent operations fail, ensuring that internal server errors are returned as expected.
