Update Rust crate config to 0.15.0

Author: renovate[bot]

Cargo.lock

@@ -23,7 +23,7 @@ actix-web = "4.3.1"
 actix = "0.13.5"
 actix-web-actors = "4.3.1"
 chrono = { version = "0.4.39", features = ["serde", "clock"] }
-config = "0.13.4"
+config = "0.15.0"
 reqwest = { version = "0.11.23", features = ["json", "blocking"] }
 serde = { version = "1.0.195", features = ["derive"] }
 tokio = { version = "1.28.1", features = ["full"] }