feat: add test_load and test_parse binaries for configuration loading and parsing

apps/gateway/Cargo.toml

@@ -42,3 +42,8 @@ dirs.workspace = true
 rusqlite.workspace = true
 axum.workspace = true
 clap = { version = "4", features = ["derive"] }
+
+[[bin]]
+name = "test_load"
+path = "src/bin/test_load.rs"
+