static WebSocketFrame ofPong() {
        return EMPTY_PONG;
    }
Returns a pong {@link WebSocketFrame}.

@see <a href="https://datatracker.ietf.org/doc/html/rfc6455#section-5.5.3">Pong</a>
core/src/main/java/com/linecorp/armeria/common/websocket/WebSocketFrame.java