feat: implement transaction handling for upstream and target operations

- 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.

apps/api/Cargo.toml

@@ -31,11 +31,12 @@ uuid = { version = "1.19.0", features = ["v4", "serde", "fast-rng"] }
 tower-http = { version = "0.6.8", features = ["cors"] }
 reqwest = { version = "^0.12", features = ["json", "multipart", "stream"] }
 serde_urlencoded = { version = "0.7.1" }
-optfield = { version = "0.4.0" }
 
 [dev-dependencies]
 tempfile = "3"
 axum-test = "18.4.1"
+agent_client = { path = "../../public/agent-client", features = ["mockall"] }
+mockall = { version = "0.14.0", features = [] }
 
 [lints.clippy]
 unwrap_used = "deny"