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.

Cargo.lock

@@ -7,7 +7,7 @@ name = "agent_client"
 version = "0.1.0"
 dependencies = [
  "async-trait",
- "mockall",
+ "mockall 0.13.1",
  "reqwest",
  "serde",
  "serde_json",
@@ -2247,7 +2247,21 @@ dependencies = [
  "cfg-if",
  "downcast",
  "fragile",
- "mockall_derive",
+ "mockall_derive 0.13.1",
+ "predicates",
+ "predicates-tree",
+]
+
+[[package]]
+name = "mockall"
+version = "0.14.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "f58d964098a5f9c6b63d0798e5372fd04708193510a7af313c22e9f29b7b620b"
+dependencies = [
+ "cfg-if",
+ "downcast",
+ "fragile",
+ "mockall_derive 0.14.0",
  "predicates",
  "predicates-tree",
 ]
@@ -2264,6 +2278,18 @@ dependencies = [
  "syn 2.0.111",
 ]
 
+[[package]]
+name = "mockall_derive"
+version = "0.14.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "ca41ce716dda6a9be188b385aa78ee5260fc25cd3802cb2a8afdc6afbe6b6dbf"
+dependencies = [
+ "cfg-if",
+ "proc-macro2",
+ "quote",
+ "syn 2.0.111",
+]
+
 [[package]]
 name = "native-tls"
 version = "0.2.14"
@@ -2465,17 +2491,6 @@ dependencies = [
  "vcpkg",
 ]
 
-[[package]]
-name = "optfield"
-version = "0.4.0"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "969ccca8ffc4fb105bd131a228107d5c9dd89d9d627edf3295cbe979156f9712"
-dependencies = [
- "proc-macro2",
- "quote",
- "syn 2.0.111",
-]
-
 [[package]]
 name = "ordered-float"
 version = "4.6.0"
@@ -5599,8 +5614,8 @@ dependencies = [
  "jsonwebtoken",
  "migration",
  "mime_guess",
+ "mockall 0.14.0",
  "once_cell",
- "optfield",
  "reqwest",
  "sea-orm",
  "serde",