Introduce structured logging

We're enabling the log crate feature everywhere, but only using it on the server for now.

Co-Authored-By: Antonio Scandurra <me@as-cii.com>

crates/rpc/Cargo.toml

@@ -17,7 +17,7 @@ async-lock = "2.4"
 async-tungstenite = "0.16"
 base64 = "0.13"
 futures = "0.3"
-log = "0.4"
+log = { version = "0.4.16", features = ["kv_unstable_serde"] }
 parking_lot = "0.11.1"
 postage = { version = "0.4.1", features = ["futures-traits"] }
 prost = "0.8"