public WebSocketClientBuilder subprotocols(Iterable<String> subprotocols) {
        this.subprotocols = ImmutableList.copyOf(requireNonNull(subprotocols, "subprotocols"));
        return this;
    }
Sets the subprotocols to use with the WebSocket Protocol.

@see <a href="https://datatracker.ietf.org/doc/html/rfc6455#section-1.9">
    Subprotocols Using the WebSocket Protocol</a>
core/src/main/java/com/linecorp/armeria/client/websocket/WebSocketClientBuilder.java