client: Enable all features in docs.rs build

Somehow I forgot to add the `package.metadata.docs.rs` section when
creating this crate. Current docs online are empty because they are not
built with all features enabled.

client/Cargo.toml

@@ -17,6 +17,10 @@ edition = "2021"
 rust-version = "1.56.1"
 exclude = ["tests", "contrib"]
 
+[package.metadata.docs.rs]
+all-features = true
+rustdoc-args = ["--cfg", "docsrs"]
+
 [features]
 # Enable this feature to get a blocking JSON-RPC client.
 client-sync = ["jsonrpc"]