public ClientDecorationBuilder addRpc(Function<? super RpcClient, ? extends RpcClient> decorator) {
        rpcDecorators.add(requireNonNull(decorator, "decorator"));
        return this;
    }
Adds the specified RPC-level {@code decorator}.

@param decorator the {@link Function} that transforms an {@link RpcClient} to another
core/src/main/java/com/linecorp/armeria/client/ClientDecorationBuilder.java