public AbstractClientOptionsBuilder rpcDecorator(
            Function<? super RpcClient, ? extends RpcClient> decorator) {
        decoration.addRpc(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/AbstractClientOptionsBuilder.java